What can i do if a payday loan company is taking money from me without me authorizing it. it seems like a scam?

The problem is, they have been deducting $90 every two weeks from my account and I had no info about this company. I finally found some on-line the company name is magnum Z LLC and when i spoke to the one guy over the phone he said i authorized it. kept stumbling on his words and when i asked for a voice record of me authorizing it he said no and i asked why he said cause he said so. he said he would report me to collections and i really don't want that to happen. I paid them more than the loan amount was which was for $300 and they still are taking money out. they said that the $90 are finance charges and that I needed to call to pay down the loan so none of the $90 went to the principal in other words. I don't know what to do. Help please.