Developer-extension problem

Hello,

I purchased an extension on opencart store. The problem is that the extension DOESN'T work (i tried on 2 servers, different opencart version and always the same).
I tried to contact the developer, which always gives an excuse like (ftp credentianls doesn't work, mess up with my server email, doesn't respond to emails, etc..). The developer basically ignores the problem - for which I do paid for.
I also wrote a comment on the extension comments and he deleted the comment. I just wrote it doesn't work and if he could help me.
I don't want to give out names but at least I want a refund, what can I do ?

Just ask a refund at opencart. Hit the contact right upper corner