NEVER ENDING PAID UP ACCOUT

Had a contract with MTN that went into arrears I as called and given a settlement amount I paid it up. The next month was called again I was told that it wasn't a settlement amount that I paid. I asked for the settlement amount and paid it. This year I'm still getting sms saying that I owe MTN. Can someone please help me out the people who call keep on going around in circles I don't understand why I still owe MTN.