Unauthorised debit order

Hello Peter, please help me. Telkom mobile debited R250 from my account in Feb and R401 in March, I have no idea what for and I don't know how they got my bank details, getting hold of them is a mission, I cannot find a contact number for them anywhere. my *** number is prepaid so frustrated that we are trying so hard to watch our spend and then boom a telkommobi debit order for lord knows what.