cell c airtime i never requested

i have a jet account and on my statements I saw they have been adding monthly cell c airtime on my account???? I don't even have cell c contract and never had. I have contacted them on several occasions and requested same to be cancelled and refunded with interest and they just said someone will phone me back. up until today no one has phoned me back. am I paying for one of their friends cell c airtime??? it is on my jet account so there is interest accumulating on those amounts who will pay that back to me. how can jet even work with these people they are giving them a bad name.