Tryto--your ex can only bully and berate you if you believe what he has to say and take his words to heart. He can blame you for his choices but you don't need to accept it. Your son is only 2 years old so you have many, many more years to deal with it so the sooner you can get a plan you can stick to the better. You have to stop engaging him because that opens the door for more crap from him.
Telling him to stick to certain types of messages only allows him to attack you. If you object to him refusing to take your son on his scheduled days--again, it opens you up to more verbal abuse as does answering his request for make-up time.
Defending yourself against his claims that you are a liar and a manipulator only gives him additional paths of communication.
Spending a year working on sane responses to an insane situation seems like a long time spent with little or no relief.
Respond only to his messages that have to do with your son and with as few words as possible. Don't get into a war of words with him; don't respond to his bullying or when he says bad things about you or your parents. Don't say anything to him about his bad choices or what he's done. It's water under the bridge now.
If he doesn't get to see his son for 23 days--it's HIS loss. I know you probably worry about your son's feelings--but at age 2 he would probably rather be with you anyway.
Seriously--limit the amount of words you write to him. The less words you say the better. For example:
Him: It's not my responsibility to get son back on schedule so I will not be picking him up this week. That's your problem so you deal with it.
You: Ok. Son will be ready (whenever next scheduled visitation is).
Him: You're such a manipulative bitch. You know I could take him just as soon as he's back on schedule. I need my time with him.
You: Your days with him are______ this week. If you choose not to pick him up at that time son will see you at (the next scheduled time).
Him: If you would take him on a suitable vacation this would not happen.
You: Silence.
Him: If you spent as much time with him as your parents this wouldn't be a problem.
You: Silence.
Him: You know he cries at daycare because he has had such a good time with me.
You: Silence.
Him: You don't care about anyone but yourself; anyone can see he is better off with me.
You: Silence.
I know it's hard and you are hurting not just for you but for your innocent child who doesn't deserve this kind of situation. I was married to someone a lot like your ex. He did some of the same things and was successful in making me feel like a victim. It stopped when I realized that he could stomp around and say anything he wanted but I didn't have to listen and it certainly didn't make it true.
When I finally could look at the situation a little more objectively it used to make me laugh at how angry he must have been to be spewing all that awful stuff at me with no more audience to appreciate it. I kind of envisioned him as that little boy in "Where the Wild Things Are" having a tantrum and causing a big loud rumpus with all the terrible creatures.
Hopefully you can eventually step outside the shit storm he is trying to send your way and see him for the spoiled, immature, damaged person he is. Don't let him steal your sunshine. Life is too short.