Randomly adding contracts to my account

MTN keeps on adding random contracts to my account that I did not ask for/approve or signed for..... my account is now 3x plus what it's suppose to be and I have been trying to sort this out for a month without any luck. The incorrect amount is shown on my account from a unrecognized number that they say is a Dual Sim, which was cancelled more than a year ago. My own number does not reflect on the statement.