Appalling service from call centre

A month ago I received an excessive cellular bill. Most notably a sudden use of cell phones on the account. Upon querying this with the call centre they told me that they would do a data certification and get back to me. They did not, I had to on three occasions phone back to follow up. The outcome of all this is that the calls recorded were supposedly mine. I dialled a number of these calls and did not recognise ANY of the numbers. It also needs to be noted that this is a data package on an iPad. We cannot make calls from this device. The final call I made, I still disputed the bill and was told that there was nothing further that could be done. I refused to accept this and requested to speak to a supervisor. I was told that they were all busy and would get back to me. that was two weeks ago and I have still not had any response. Unfortunately I do not have a lot of time on my hands and am now asking if anyone else has experienced similar problem and how or what sort of legal recourse or direction I have to take.