How to deregister imessage if my country is not listed?

Question is self explanatory, but still...

Somehow, my tel number is stuck as registered with iMessage, so I cannot activate iMessage via my iPhone, thus I cannot switch it off. Activation lasts for days and never finishes (successfully)...

My country is not listed in Apple tool... Of course, there is no local apple support, physical or online.

Any other ideas how to deregister a number?