Bad service

I took access facility and the money is deducted every last day of the month, so the money has been deducted but it has been 3days now they keep on sending me messages that I did not pay, and there's a certain amount taken from the amount that I didn't use so called interests because I didn't pay the monthly installment. To cut the story short the money has been deducted but still they say my account is in arrears. I called them and I also went to the branch they're not helping. The worst part is that they say pay like for example R25 month end , they deduct the money on the last day of the month and they take interest in the amount that I didn't use and they keep sending messages that I didn't pay. The bank statement shows that the money has been deducted