Extra amount charged for handset which we did not received

We have upgraded in beginning of 2017 and since then an extra amount is being deducted on my account for a handset. After various attemps to resolve this and call backs put in on the web site nobody helped me. Therefor I am still paying for something that I did not receive. I cannot stop the payment then the other services will also be stopped. The service is extremely bad and nobody who promised to come back to me did it.