Double debit

I have had my account for years with teljoy. Never had problems. I took ownership of a device at end of January. This month teljoy still debit the full amount. I phoned them and they said sorry they haven't updated the debit order amount. Two days later they debit me with the updated amount. So I phone them and they said the collections department would phone me back in an hour. Still haven't heard anything back. So basically I have paid for my current device twice as well as a device I took ownership of which has been already closed.