Harman, this is just another example of how he still wants to exert some form of control over you all. He's smarting because he didn't get the final say over which school the children attend and so he wants you to pay for that.
I agree that you should write to him, copying his solicitor (provided you don't still have your own solicitor acting for you), stating that the change of school was initially a joint decision (evidenced by his call to the new school about the name the children would be known by), although he subsequently dithered about it and was made with the best interest of the children in mind. That Wednesdays have always been his contact day and that, as you have had to make arrangements to accommodate the new logistics, then he will have to do the same. Explain that you have new commitments on Wednesdays (you don't have to disclose what these may (or may not!) be) and will therefore not be available to pick up from either school.
If he calls on Wednesdays, I'd let the call go to voicemail, although if the school calls you can still answer - you couldn't do that if your phone is turned off.