Am I the asshole for telling my family about what my Mother did to me?

Hi Two Hot Takes, been a long time listening but first time poster… I need advice.

I 24 M recently cut off my Mum and told her family about what she did to me during my childhood.
I don’t & have never had a good relationship with her. I have tried for years to mend our relationship and tried to change her behaviour but realised it was a waste of time.

Anyway,
My fiancé and I recently went on a trip to visit my Dads side of the family, which is about an hour away from where my Mother lives. We had travelled 6 hours at this stage and had already agreed that we wouldn’t be seeing her. I was adamant on that.

Somehow, and I haven’t found out yet. She had been told that we were there and proceeded to ring me over 100 times and left 50+ voicemails where she told me how horrible of a son I am, how I’ll never be enough. You get the gist.

I decided to ring her back, and told her that this relationship is over and I’ll never be contacting her again & from now she is blocked. She did not react well, as per usual but I blocked her number and haven’t heard anything since.

Now… here’s where I MIGHT be the a$$hole.

I rang her sisters, who have lived together for a long time & told them EVERYTHING about my childhood. From every argument, every physical altercation we had, all of the emotional distress & what she said in multiple voicemails.

I had photos taken of my body as a child when social services got involved which I showed them also.

They were shocked, and said they didn’t know this was going on (it’s a lie but I’ll let that slide)
They have since been in contact with her and told her about what I said, she of course denied it but because I had physical proof of it.. she could only deny it for a short time.

They believe her side of the story though & are now trying to convince me that it’s “all in my head” and that I should forgive her because she’s my Mum.. the old saying “you only get one Mum” stuff.

So reddit… am I the asshole for cutting off my Mum and telling her family about it? If not, how do I deal with this situation to help them believe my side of the story.