I can think of two ways to permanently prevent one from posting on Gransnet, two ways within the bounds of life and reason, of course.
One is to get one's IP address on HQ's banned list by sufficiently annoying them.
The other is for Gransnet to be banned in its entirety. I think we'd have to live in a military dictatorship for that to happen and even then it takes a stretch of imagination to wonder how a bunch of grans chatting about stuff could even get on the dictator's radar.
There are loads of other online talk forums though. So again, if one finds them stressful for whatever reason, the problem is one of self-discipline or, to put it another way, might be to say it's one of addiction control.
Wish you well, jura, but as you see from my comments above, it's really up to you. I'm sorry it's an issue.