So a bit of background first.
DS is 12 and just finished year 7. For most of the year he hung out with the same two boys, x and y. Towards the end of the school year DS became friends with some other people. At first there was no big fallout between DS, X any y they just weren't the close 3 they had been. But then x took a dislike to DS's new friends, slagged them off and DS stood up for them. I think they had a physical fight, to me this is both of their faults and I admonished my son for it.
Now x has phoned DS twice this holiday. First time from a withheld number, with another child in the background. X told DS nobody liked him and he has no friends. Then today x rang DS again and called him a twat, said no one likes him etc.
DS is actually ok about it, quite philosophical, has said he could block him but then x would think he was getting to him.
I think it's properly nasty behaviour, but I'm not sure what to do about it. DS doesn't want me to do anything. DSis thinks I should ring/text mum asking to meet and sort it out between the 4 of us. I'm more tempted to text her asking her to ask x to stop phoning DS, but don't want to go behind DS's back. Not really an aibu, more of a wwyd?