I've contacted "support" but I dont think they are managing that mail at all since I never get any reply at all from them, something I'd expect at least.
You mean uCoz Support? When did you do it? It can take up to 48 hrs to receive an answer but usually, in around 24 hrs you should be getting a reply.
Regarding the domain attachment, you purchased a domain from domain.ucoz.com and want to attach it to a non-ucoz website?
If yes, then you must take these steps:
1. Log in to domain.ucoz.com
2. Go to "Domains" section
Follow the instructions in the Screenshots below:
If you want to attach the domain purchased from the domain.ucoz.com to a ucoz website, you've got a full tutorial and instructions here, in this link. Hope this helps!