Advice needed please

My son who is 22 was diagnosed with autism around the age of 4

when he was 3 his mother cheated on me and married someone else and had another child

when he was 9 his mother committed suicide so he came to live with me, unfortunately I was sent to prison so I left him in the care of my parents as his step dad is a bully (the reason his mother committed suicide)

Since being released from prison he hasn’t wanted to know me so I’ve not pushed for contact but still buy his birthday / Xmas presents

for the past month or so his behaviour has become unbearable, he keeps banging his head punching himself smashing his stuff and ripping his clothes

my parents have contacted SS but at the moment they have only contacted them by telephone

can anyone recommend anything that can be done to try and help ?

thanks