Dear Aberdeed,
You have attended the conference, but you could refuse to pay, if you did not want your paper to be published by them. Why did you pay? You could refuse, did not you? If I were you, I would say I did not have the money, and did not pay.
Another question: why did you give the copyright to them? In my opinion, it is very unusual, as I never transfer a copy right to present a paper in a conference.
