Unprofessional and theft

I had a data contract with Telkom and it expired and they offered me new contract, which I took. My problem is that they are billing me twice for a new contract and the old expired contract. How can they bill me something that I no longer have? Worse part they billed me during the month. And I can't reach them because their lines are not answered. This is so very unfair, unprofessional. And it amounts to theft. You can't bill the same product twice.