worst service provider!!!

I have three contracts with mtn in may I went to the gateway store to make a payment the guy then told me I was in credit for may n I didn't have to make a payment I then next day went back to make sure and he said the same thing I then believed them but after that in July I received a bill stating I have an outstanding balance of R1200 and something upon calling mtn customer service and billing department several times nothing has been done the first time the girl I called said mtn made an error and will callback in 24hrs n sort this out no1 contacted me I called again another lady said I will be contacted because it's mtns mistake n they will recalculate the bill n put the right amount still no one contacted me I then phoned again and was told the same lie some one will assist me soon mtn is full of nonsense I will never in my life go with them again and I will like this to be sorted out asap before I go any further because I'm sick and tired of calling people who doesn't even understand ur query and keep been told the. Same lie over n over I need this sorted out asap I'm very upset with the appalling services I have received from mtn and will never. Recommend anyone to them