You missed this bit:

> after a bit of an ear bashing

If someone from my old employer calls and asks me politely for a bit of help with something I know well, I'd help.

If they call to yell at me about how I left behind a fragile system or how I left them in the lurch by quitting, the correct response is to tell them to get fucked, if they then ask for help after that, the correct response is to tell them to go fuck themselves.

Normalising that kind of abusive behaviour is not going to improve the lives of the co-workers you left behind.