From now on every week just tell him, "I'm available on this day and this day at this time through this time. If those don't work for you, provide me dates and times when you are available and I'll do my best to make it work." That's all you need to say then take screenshots of his responses, print them out and save them in a folder. Do not reply to his snarky responses with anything other than "I'm trying my best to make sure you have a relationship with your kids but if you don't want to spend time with them, that's on you. Don't regret it later." Take screenshots of his reply and save those as well. If for any reason you need to go to court, those screenshots will help you, also if he tries to poison your children against you (which it looks like he is doing by blaming you for his absence) you can also show them the proof of your many attempts.
@Ciara not currently.
@Kimarys that's another thing I don't look forward to. If he does those remarks on the phone. Don't put it pass him to do it in person.
He won't take responsibility for his actions (or lack there of) and will blame you. He's already doing it and will continue to do so
Does he have a car