Mtn review

I have had a phone contract with mtn for the past 2 years or so. Everything has been going smoothly. I have been paying via the mtn app and have not had any issues until end of last year till now. I have been trying to make payment via the app but I keep receiving calls from them saying I have not paid my account and they have now blocked my number. I have been making payments every month and When I call to find out the issue, I am told to email my proof of payment, which I did but my number is still blocked. I am not sure what is going on because I can’t be calling them everyday to hear the say thing. When I try make payment again the money just bounces back into my account.