Hell service

How frustrating does it have to be. Its been going on for a year now that they deduct money from me on the 16th which is payment for 2 months every time. I called to complain about it but nothing happened even yesterday I called to question and them handing me over. The contact stated last day of the month with the payment of R645 but several times I have to be deducted R 1380. Can this be stopped.