"I wanted to fall back in love with you again. You deserve to see the sober Mark."
Wow. This is so presumptuous of him. He's thinking 100% of himself here. HE wants to fall in love with you again (but he doesn't love you now, he's just toying with the idea of maybe loving you in the future)... for what? Was his idea of "being in love" good before? Or was it just about you looking after him? It's the "again" part that's not great here. He wants the same old "love" that you supposedly have... one where he probably did no work and you all the work in the relationship. By "work", I mean emotional labor.
If he really is in recovery, he would not be asking anything of you, or telling you what you need or deserve. This conversation you had with him does not sound remotely like an apology. "I owe it to you to be the new Mark who treats you well" = "I owe it to myself to tell my ex that I'm an awesome guy now".
Also... you "deserve" to see the sober Mark? Come on. This guy... . He's telling you what you deserve. If he knew what you deserve he probably would not have done the things he did to you in the past. What's the chance that he knows how to treat other people the way they "deserve" now?
He talks as if he's only deigning to pick up the phone and call you, like "allowing" you to hear his "sober" voice is a big huge favor. I think this is what he was really saying when he called you: "Hey Mandy, it's me, Mark! Remember me, the guy you dumped? I'm sober now, woot woot, check out the BRAND NEW awesome SOBER me... and then watch my @rse as I walk out this door!" I'm making assumptions here about him being vindictive. I really don't know him... and have not read your past posts. I also think that accusing you of seeing someone else is his way of telling you that he's seeing someone. I think he called you as a "back-up"... because whatever behaviors got him into his addiction are probably causing trouble in his new/current relationship... and he needs a backup. This is all from the classic A's playbook. I don't know anything about Mark here. But I would not be surprised if this was happening.
I knew an A who could turn on the waterworks to draw you in, because you think he's being honest and vulnerable, and as soon as you're close enough, his mask will drop and he'll scream at you about how you've made him a victim by staying away from his madness.
No contact = no new hurts. So easy to write, so hard to enforce. I understand why you called his grandma. I would be curious and do it too... or at least be very tempted to do it. I think if I didn't, my brain would keep trying to think about why he called... and it would drive me crazy. Forgive yourself and move on. You slipped up so be kind to yourself. Take a long bath and have a cry. Be strong. If you need a stock reaction to these unexpected phone calls from Purportedly Sober Mark, I suggest screaming (Arrruuuggghhhh!!!) into the phone and hanging up quickly... then speed dialing your local snake control to come check out your home.