Is it possible to communicate thru email instead of the phone? That way you could ignore the BS and still address the business. If not, then I would suggest ending the conversation whenever it goes 'out of bounds.' You get to decide what 'bounds' are, not him. You can do it in a nice way--the kids need me, someone's at the door, late for an appointment, whatever. Pretty soon he will figure out what the limits are.
As far as the check goes, he can't cash it either, right? Two names requires two signatures, so it's useless to either of you without both? If you can, I would just wait him out on that. When he learns that he doesn't have the power over you he thinks he does, he'll likely give in. That was my experience anyway. The more my XH knew I wanted something, the less likely he was to cooperate. If I simply acted like it didn't matter, he stopped digging his heels in.
I really feel for you because I know how frustrating it is. The good news is that you are going through the hardest part. Once it is legally over, his power is gone. He probably realizes that, so is making his last stand.
Bubble bath? Pedicure? Funny movie?
Hang in there. It will be over soon.
L