wrong billing and bad service

I had a corporate contract with MTN for R550 which stated in october 2013 under Gauteng Department of Finance and wheni left the department i worked for i took over the contract. It was for sumsung S4. 3weeks ago my phone was closed and called MTN and i was told i owe R6500 i disputed the figure because i knew the department had been paying, i asked what constituted that amount a Ms Mbali Ndlovu said that the department had been paying R500 for the airtime and i was suppose to R250 for the phone i dispituted as i knew very well i only qualified for R500 in the department and i asked them to give me my contract which they did and it proved exactly what i told them but the matter was not sorted instead Mr Mlunjwana said he was investigating the matter but never gave me the outcome oh his investigation instead he was lying to me and avoiding my e-mails. after 3 weeks of not having a phone i decided to pay MTN so my phone can work even though i was right, when i wrote to Mr Mlunjwana that i wanted to pay that's when he started calling me and responding to my e-mails. I'm disgusted at the way i was treated i decided to refer my matter to the ombudsman and consumer watch.