I have never had a contract, but I owe money?

For the past year MBD Inc sends me sms after sms about a Cell C contract that I have no knowledge of. The attorneys have phoned me numerous times threatening with legal action. They can't supply me with any details as to when, where or how this contract was initiated. There is no Cell nr, no usage of this contract and no handset or contract documents. The details they have of me is incorrect accept for my Vodacom contract cellphone nr. What do I do? Nobody at MBD can give me answers. The details is as follows : *** Ref ***. According to them I have to find out where the contract is and I must prove that I do not have a cell c account. Please help me with this as i am frustrated beyond myself.