There has been almost 400 percent increase in unsuccessful attempts by sex abuse victims to get mental health support over the past 15 months.
In that time survivors have tried more than 10,000 times to get help but were rejected.
Those who manage to secure a booking face waitlist times that have more than doubled.
ACC says it comes down to a lack of capacity among its sensitive claims mental health service suppliers.
Services at capacity - 'It's so disheartening'
Earlier this year Wellington woman Cassandra Saunders made the tough decision to seek mental health treatment for historical sexual abuse.
She contacted every mental health supplier and multiple individual therapists on ACC's accredited list for the capital - dozens and dozens in all - and got rejection after rejection.
"[They said] 'no we don't have space, no we don't have anything'. It makes you want to cry because it's just so disheartening knowing that even if you want help there's no one out there that can because their load's already too big."
Saunders said it looked like her best option was on a waitlist for an appointment up to a year away, or sooner at a different provider if she was willing to have a trainee psychologist sit in.
She did finally manage to wrangle an appointment - though lockdown put paid to it.
Wellington Rape Crisis general manager Kyla Rayner said demand was unprecedented.
"It's at the highest that we've ever seen in the history of our organisation. I've been in this role five years and the agency itself has been around over 40."
Grim stats show system 'failing' survivors
ACC's national waitlist figures indicate that failed attempts by sex abuse survivors to get mental health help increased by 387 percent and reaching 4131 in the most recent quarter from 847, 15 months ago.
Sexual assault survivors' calls to suppliers to try and get mental health support were rejected more than 10,000 times in the past 12 months due to lack of capacity.
Many sensitive claim mental health support suppliers simply do not have room on their books to take more people on.
In fact, referrals were declined 2.8 times more often than clients were actually placed onto waitlists.
Weighted average national wait times have more than doubled in a year to more than 9 weeks, from 4.3 weeks.
Waitlist times are far longer in some places. In the three months to May average waitlist times stretched up to 25 weeks in Lower Hutt, 22 in Nelson, and 20 in Masterton.
The size of waitlists have also grown. The number of spots claimed by people has more than doubled, up 124 percent in the past 15 months - from 656 to 1473.
Green Party ACC spokesperson Jan Logie said delays compound the harm to survivors.
"Flashbacks, nightmares, terrors, really struggling to keep functioning.
"And to get to that point and then [survivors having] to make call after call after call to [suppliers and they say] 'sorry ... can't help'.
"It's an absolute failure of our system."
ACC has doubled therapist numbers, but demand skyrocketing
ACC said the figures are a snapshot provided by services as part of a quarterly survey, and do not include people who get immediate treatment and avoid waitlists altogether.
Only a third of suppliers offer a waitlist.
The numbers also represent attempts to get access to services, not individual cases, and people likely make many attempts for support from multiple providers.
ACC said annual sensitive claims have more than doubled in five years to nearly 13,000, jumping 20 percent each year since 2014.
It has more than doubled the number of sensitive claims therapists in that time to 1990, with nearly 500 coming onboard in the past three years. It has also made it easier and faster for suppliers to bring on new therapists.
There is a nationwide and international shortage of mental health providers and this workforce challenge is something ACC says it is unable to solve on its own.
ACC said it has not been able to close the gap between supply and demand.
"Media coverage, the #metoo movement, the Royal Commission of Inquiry in Abuse in Care investigation, societal trends, and awareness-raising prevention campaigns are changing attitudes towards sexual violence, which we believe is resulting in more survivors of sexual violence feeling they can seek help."
Rayner from Rape Crisis said while New Zealand has high rates of sexual and domestic abuse, attitudes have also changed.
"In some ways it's kind of positive to see that so many people are coming forward because that's the reality of the prevalence of this harm in our society. The problem is now we're trying to catch up."
But Logie said ACC has known about the problems for years and has simply failed to take responsibility.
College of Clinical Psychologists executive advisor Paul Skirrow said the increase in therapists touted by ACC might not tell the whole story.
The mental toll on clinicians from working with sexual assault survivors meant many only worked part time, he said.
"There's actually ACC guidance that says that you shouldn't spend more than 50 percent of your time doing this kind of work. So we're talking about a number there but that might be a very small number of appointments available that it might translate to."
ACC said all survivors were entitled to 14 hours of one-on-one therapy, and 40 hours of other support after an initial assessment while they were having their claim analysed for possible full, long-term cover.
Those in crisis could get support from the wider mental health system, it said.
Where to get help:
Victim Support 0800 842 846
Rape Crisis 0800 88 33 00
HELP Call 24/7 (Auckland): 09 623 1700, (Wellington): be 04 801 6655 - 0
Mosaic - Tiaki Tangata Peer support for males who have experienced trauma and sexual abuse: 0800 94 22 94
If it is an emergency and you feel like you or someone else is at risk, call 111.