Underneath he is still the little tin god he has always been, the "nice" is only skin deep.
Just because he forgot what you told him, he goes off his tree and lays it on to you.
I know you need to keep contact with him, but the first unpleasant words over the phone could be your cue to HANG UP immediately, and not answer further calls from him.
As for text messages, send the first nasty one back to him, and ignore any more.
No law on earth says you need tolerate or be hassled with offensive material.