Incorrect billing

After my previous report dated 10July 2015 the response I received - they called me on the 15 July and said it was their mistake they did not do a top-up contract and I used the data which I was not aware of and they would give me credits on my account for the inconvenience. The 16 July I received a final demand letter stating that they were going to hand me over to debt collectors. I have never failed to pay my billing. I received their statement with no credits and some payments not reflected on the statement that I hve paid. This is now going from bad to worse. I will get legal representation if I must to sort out this problem once and for all.They are not doing their job as what they should. I need someone from Autopage to come back with positive results. At this time my phone is still suspended.