***** contract that I never had

I have been receiving calls fro iSmart, been told its regarding my account. I'm surprised because I never had a cell phone contact with them and they keep calling me. In the past 12 years I only ha a 2 year cell phone contract with cell c and it ended in 2011. So this ISmart thing I don't even have a clue who they are, and I plead again, please stop calling me I have no contract with you and never had. I asked to be provided with the details ofwhen was the account opened and they put the phone down. So please remove my number from your system.