My ex boyfriend left me badly and said things that hurt deeply. Ive had no contact for 2 months. Then he texted me on the day that shouldve been our anniversary and said that he really felt bad for the way we split up. I didn't text him back as I don't have anything to say and I still feel really hurt. But only from that one text feels like I have to start the hole healing process over because I am back to square 1.

I think you did the right thing by not texting back. I'm sorry you didn't change all your contact information.
Try not to think in terms of starting from square 1. Try to get some small amount of satisfaction out of the fact that he misses you, which means he has to be feeling some degree of being wrong. Who knows; he might just be selfish and maybe some girl ditched him recently. Pretend that's what happened, just to drum up some anger instead of hurt all over again. Healing requires anger after hurt. 'He's no good, he didn't deserve me, I hope a thousand women run him through the mill' etc. Be angry, and then let it go. The key is to not stew in the anger. It's just a tool to get past hurt.

You are not starting over, just continuing with what you started. His apology changes nothing, but does give you the satisfaction at least that he handled himself badly, and knows it. Stay with NC, block him from further contact.