To think he has to communicate at some point?

[PostmanNat]

2 years ago my ex left me for his best friends sister (I kind of had a gut feeling it was happening but I was so busy with the kids)

anyway, since the split he has blocked me on all avenues, I don’t know where he lives and cannot get hold of the children when they are with him. They are 5 and 8. He even refuses to come to parents evening with me.

I don’t know where ex lives either, I have a rough idea but I’ve never pushed it. I don’t care to have any contact with him or know details about his life. HOWEVER, dd is old enough to have a phone which is kept charged and she can keep in contact with me during the odd time she spends at her dad’s. And if I was to ever move, I probably wouldn’t disclose where we lived to him. We don’t like each other.
If you don’t want to accept the status quo, an option would be to self-refer to a family support worker to see if you both could engage with them and reach a less toxic understanding. Honestly I’d only bother with this if 1) your kids are too young to communicate with you 2) you have genuine concerns about his parental ability.