Contract expired and over charging

Contract expired in November of 2015 but I was still billed till January. I went to them to get an understanding of why they continue billing me but I was given the run around being told that it's billings fault when I asked billings number they refused. In February they line was finally converted to prepaid however they started over charging me. I was charged 1334 for the remaining lines and I had never been billed so much before when I had more lines.i ended up getting hold of billings number spoke to nokuthula who advised me to reverse that money and pay 687 than I went back to southgate to get the telkom bank acc number to make a manual payment and the statement that I got for my account reflected that I had a credit of 195 two weeks after that all remaining lines were suspended and they said I owe them 687 and I paid it on 25 February 2016. On th 29th the debited my acc 1177.58 than went back and spoke to the manager than he said I had to pay 492 and not 1177 I paid the 492 and reversed the one debited and today I received a statement saying the total due for the month of March is 1045.80 and according to mi knowledge I have to pay a total of 555 for the lines remaining.