payday loan

My husband and I decided to get a pay day loan from the little loan shop to help pay for christmas shopping expenses. We maid arrangements to pay 35 to extend our 300 loan until January. After making our first payment of 105 we made the decision to pay off the loan completely. they were suppose to debit the entire loan amount and interest. Since then they have taken over 600 out of my account, they refuse to produce the supposed contract we signed, and are now telling us we agreed to make 20 equal payments of 105. This is ridiculous and I don't know what to do. They have already taken more than agreed upon and have scheduled more payments to be debited from my account. I have no idea what to do.