Are "interest only" payments ok?

I got an online loan from a company called CK Marketing. For the last 2 months they have taken out $75 from my account every pay day. I thought I was paying towards my loan. I just got off the phone with them and was told that I was making "interest only" payments and that I still owe the entire loan amount and that they are going to continue to take out $75 each pay day until I pay the loan in full. Is this ok? I am very frustrated and am hoping there is something I can do to keep my money. I got the loan because I needed money and now they are robbing me of it!!!