Is it really their job? As far as I know they're not responsible for any trading going on here.
While it's not, they facilitated getting scammed via chat when they removed basic user info, like registration date and rep, and using all caps. The least they can and should do is restore the above to the state they were when we had the PM system.
But judging by their brilliant
idea of how a blocking feature should work efficiently (first add the person you won't nth to do with to your contacts list, and never be able to remove them), that's probably too much to hope for.
Or you could start spamming GOG staff with complaints via chat, twitter, e-mail, YT comments... until they do their job. Just sayin'
I've often thought that perhaps the only way to make GOG listen is to make things like these public outside the forum, as they don't seem to care about their image being hurt in here.