MTN cellphone contract

I have a contract with MTN for a cellphone,data and minutes.i lost a SIM card which I have a contract with MTN gave the phone number to someone else while I paying my account using the phone number as a reference, the second person took a contract as well on the same number and now MTN have signed a contract with 2 different people using one phone number and we are paying for data and minutes on the same number. Iv tried to sort it out they just tell me that they deal with sales