List me as a bad payer

I received a invoice on the 1st of November 2014 for an amount of R4 671.50. My average invoices from them in the last 2 years where never more that R1 800.00.According to them it was data usage. I stopped my debit order and was told by a call centre lady to just pay the contract fee until this query is sorted out, which I did every month. I then logged a query for the data usage. I filled in forms on the 23 of December 2014 and again in January 2015 and haven't received anything back. after numerous phone calls I always get the same answer from the call centre they can see the query is logged but there are no response yet. I have a Samsung phone that shows you the data usage on your phone and it always differ from their charges on my invoice, when I asked them why I got no answer. I then wanted to upgraded and was told that I need to pay the full outstanding amount before I can upgrade which once again I did. I also re-instated my debit order. I app**** for a bond and was told that they listed me as a bad payer so the banks declined my applications. They now have all there money, I have a bad record and still an outstanding query with them.