How do people seriously co parent with toxic ex's 😤

So I have 3 children with my ex who physically and mentally abused me for 10 years. He has been in and out of the kids lives since day 1 even when we were together he refused to live with us and would turn up as and when it suited him. Our son 8 basically started acting out and being a danger to his siblings because he wanted to permanently be with his dad so he didn't have to constant worry of when he will see him again. I made the arrangements (his dad was not to pleased but agreed) well he stayed over at mine for the weekend like normal and turns out his dad went on holiday and didn't bother turning up to collect our son so I told him he is staying with me because he can't keep missing school whenever his dad chooses not to show up to get him and he can't be coming to my house worried if his dad will collect him. His dad then tried to control me by saying he will refuse to pay maintenance (it was going just between us no agency we agreed he'd pay the amount the agency suggested and once a year he'd help towards their school uniform ready for the new school year) and has also refused to see any of the children again (done this numerous times for months at a time)

This was the last straw for me as Im sick of him mentally abusing my children so I decided to do our maintenance through an agency so he could no longer use it to control me and so we didn't have any need to have contact. Well now he's pissed I've done maintenance through the agency and is refusing to help towards the children's school uniform i know he doesn't have to and it's a good gesture that he did but with our son moving back in I've had to buy a new bed as when he moved out i let my toddler move in to his bed and he shared with his older brother the nights he was here (2 nights every other week) until we moved into our bigger home where there's more space for his own bed to fit. I've had to pay for my son's school trip and all new clothes because his dad refused to give his back which I paid for so I'm just not in a position where I can buy their uniforms without the additional help