(Sorry for any mistake, i'm not a native speaker)

Hello. I'm sorry for the situation
I can relate a bit, since I also refused to stay in contact with my family in the past years (i was very introverted and suffered from anxiety and low self esteem) and I'm totally regretting it

I think it's a delicate situation.
It seems your son is disappointed with his life and angry, so how could you talk with him?

If you think that in general he's capable of affection (and "just" facing a really difficult time), maybe you can send them message and write him that you care about him and that he can count on your help. Sometimes people are nervous and get easily angry durings calls

Do you have anyone to talk with about this problem? And does your son have any close person (a girlfriend, a friend...)?

Big hug