Bad service not professional

I am very disappointed at how mtn treat us as customers.first I complained numerous time about their service but they don't want to improve at all I have a cell phone contract with them a top up that I pay R288 but suddenly they send me a statement saying they have increase my installment without even informing me I just saw that my account is in arrears and they never resolved it at all. Second time I complained abouty airtime I will have like 10 rand in my account it will not call and say that I have insufficient fund to make a call when I check balance I have airtime I loaded data same thing it will say u have no data until the data is gone they will tell me their record shows I was using internet and it's lies they never been bother to refund me instead they blamed me.lastly I paid my account on the 01/11/15 with easy pay at shoprite coz I was at Limpopo their mtn branch most of them don't want to receive payment they will tell u to pay at bank or easy pay which I did n now I received an SMS saying my account is overdue I should pay to avoid bad credit record while I paid long ago and phoned them 6 times still they are telling me they can't c my payment needed to send proof.