Glancing at my inbox and trash folder, last bulk of endless GoG emails was in December of last year. So for the moment i'm not getting bombarded by endless emails; That or the cache of those emails already were purged, not sure. Or maybe the email server finally removed my email from the subscription list. Maybe i'll be lucky and not see further spam.

But i doubt it. When it starts again, no doubt it will be a flood.

I understand your frustration. It's essential to contact GOG's customer support for assistance in resolving this issue and ensuring your preferences for promotional materials are respected.

I might change mail duo all the spam

Before changing email addresses, have you confirmed in your settings (via Themken's post above that all email marketing is turned off? That would be the first step in my opinion.