Urgent help please - kids on holiday with dad in another country

[FarquarKumquatsmama]

Divorced for 5 years plus. Ex-h has a history of violence towards me and the kids. No violence for a number of years. Volatile relationship with DC1.
Kids FaceTimed me with sunburn earlier. I told them to keep out of the sun. Ex-h tried to get them to go back to the beach and they said no and said I told them not to.
There has been a big argument between my kids, esp DC1 and their dad. According to my kids he tried to throw a tennis ball in the face of DC1.
Kids are very upset, ex-h sent me a very angry message about not interfering in their holiday, I called and he has got very cross with me and now banned all further contact between me and the kids while they are away with him.
Is he allowed to do this? Should I report it?
I thought of maybe giving him until the morning to calm down and be reasonable and then trying to discuss with him again and if still not success, then report.
Are there any rules about blocking contact?
My heart breaks for my kids.

[TypingoftheDead]

Good luck, OP. I’m rooting for you!