Gosh, he’s really showing his true colours now, isn’t he! Was this by text/whatsapp? I’d use this as an opportunity to say that, in order to avoid any more confusion/nastiness, he needs to assume, barring genuine emergencies, that you are otherwise engaged when it’s his time with the kids and that he has friends and family that he can call on to help him with babysitting/lifts/to lend him a tenner for potties etc - plus ample free time in which to sort out car repairs, haircuts, tattoos. I would spell out again: you and he are no longer each other’s support (practical, emotional, whatever) and the sooner he adjusts to this new reality, and stops thinking of you as someone who’s there whenever he can’t meet his parenting obligations (which he has asked to comprise 50% of the kids’ time), the sooner he’ll be able to behave towards you in a calm, non-abusive manner that is conducive to good co-parenting. Until such a time, you insist on all communication to be via text and limited to sharing only necessary information about the kids’ wellbeing. Any requests to change times at short notice should be for emergencies only (though ideally, unless it is the kids needing you, his support network - of which you are no longer a part - should be his first point of call, not you). I’d reiterate that for you, mediation is a preferred next step and ask him to let you know when he’s ready for that, but in the meantime, he’s need to refrain from verbally abusing you.
What a c**t!