Bad bad service

I receieved a statement in the beginning of Jan 2015 that i had asked from CellC which showed that my outstanding bal was R2126.68, i then made a payment to Cell C for R1000.00 at the end of Jan 2015 and then made another payment of R1126.68 at the beginning of March 2015. Later in March i receved a call from a lady by the name of Salomi Govendor from a company called MMM Capital which is a collections company for CellC, this lady informed me that my account was escalated to them as i had failed to pay and my outstanding balance was currently at R1700.00. I requested for a statement in March 2015 which had a break down of the fees that had accumulated for the balance to be what it was as i had already made the 2 payments, she then sent me a letter(not a statement) on the 30 March showing that my bal was R2,730.41 however during our tel conversation it was at R1700.00 and when I queried this bal she told me that it was ann error they made and my bal now was at R1603.73. I asked for a statement again which she only sent to me on the 17/04/ 2015 which did not have my name nor my cell phone number and also was not on the CellC letter head nor their company.