EX h and I have 3 young DC.
We've been divorced for a few years, he had an alcohol problem and was emotional abusive to eldest DD.
All was well between us at first, although he introduced DC to 4 of the 6 GF's he had in the first 6 months, one of who left weed lying around his house.
He then moved in with my mother (who took his side through the divorce) but has now bought a small flat.
I am in a serious relationship and am 8 months pregnant. EX has been in a serious relationship for a year.
I realised he had been massively underpaying me child maintenance and now owes me over 1K which I have had to write off. He has done numerous other underhand things which would be long and boring to detail. We have been having problems arranging access, he has them a few days a week but puts them in childcare most of the time 
He has been completely stonewalling me for the last month, sending the DC without their coats or shoes (I collect them from school rather than his house) and refusing to answer any of my messages when I request them.
He refuses to reply to important messages about the DC ( I don't speak to him otherwise) both when they are with me and with him. He just completely blanks me.
I am now heavily pregnant and his behaviour is making me feel ill. I feel like just not sending them back to him but obviously I wouldn't actually do this because it would only upset DC...
Just want some views really..