Account Conducted In a Pathethic Manor!!!

My Girlfriend and I have a contract with MTN and she even has a prepaid number with them as well. We have been having issue's from October 2014 and have visited the cresta branch on numerous occassions. I have been paying this account every single month without any hassles or issue's. However now in February they cut of my conta ct and advise us that we in arrears for R1500+. This is utter ********, I have visited the branch and provided them with soo many proof of payment, They then tell me that they can't locate the payments and a whole lot of ******** excusesd.....Now i need to visit the Headoffice to resolve this....This is utter nonses and is costing me money for running around....getting bank statement for the 4th time....I plan on changing networks to Vodacom due to the pathetic service received!!