Should a Son disrespect his Dad and family over a social website and insist he sees his grandaughter?

My son recently and continually places harsh rude abusive messages on a social website about his friends and Family , Mainly directed at his Dad (me) and his Sister, quick outline , his mum and I separated some 18 years ago now ive re married and have 2 step children , my son is 22 and has a girlfriend 23 and my granddaughter nearly 2 , my son has had a chip on his shoulder for a number of years now and is fore ever falling out with members of the whole family but mainly me and now his sister you see he complains on the websites and via text that we never go to see him or make any contact with him he says we never ask about his daughter and that were not interested this is his normal pattern , in truth we do bother and contact and see when we can both myself and his sister work full time and I myself have 2 younger children that I see every 2 weeks or so 13,and 12 there ages boys so when I pick them up I often arrange to carry on and see there brother in the same day but he often cancels saying his girlfriend wants to go out as shes worked all week , in six years of me being re married he has never once made his own way to my house to see us I have always picked him up and taken him back 45 min journey each time , the final straw was when he called me some fairly nasty names on the website and threaten to tell secrets??? , I really have no gripe with my son but I cannot continue to allow him to destroy me or his sister in this way out of the 6 children in my life he is the only one who continues to cause this kind of grief they have all been through similar problems but do not behave in this way , im sorry to say his girlfriend is of similar character and I think they both rub each other the wrong way and then join together when its someone else , I m at a loss now as to what I can do at the moment I have cut ties with him taken him off my social web page I have the others and my wife to think of , any advice would be greatly received and a final note I was told his final message to me was he appreciated the help I gave him in trying to get the wages he was owed when he broke his knee but when I couldn't get it I didn't put my hand in my pocket and help , that just summed it up for me