Mtn paid up account

I am disappointed with the service I am receiving from Mtn Sa it's actually frustrating. I had an account with Mtn and I requested a settlement letter to settle my account which I waited for almost a month to get it, as soon as I got tge settlement letter I paid off my account and also required a paid up letter which I received. I called Mtn about 2months back to change my contacts from contract to prepaid then I was told that I am still owing on my account and I couldn't understand because I have a paid up letter.. I requested for the team leader or accounts manager to contact me and I am yet waiting for the call. I am frustrated because I settled tge account for a specific reason, I app**** for a home loan and I am not supposed to accrue any credit till the application is done however this might affect my application. Now I am receiving an email stating me to pay with a differ acc number and reference number from the one I settled with and if I Don't pay I might be in arrears and and it may affect my bond application. I am furious at this point because it has been 2 full months waiting for someone to explain to me why it is this way.