Incorrect Billing of Account

I have logged a complaint on the 12th of November 2018 about the incorrect billing of my account. I have contacted the call centre about seven times since November to try solving the problem. Every time when I contact them, I must explain the problem over and over again, and every time the same answer we will escalate the problem the supervisor to assist and that he/she will get in contact with me still waiting for that call. On the 28/01/2019 I have contacted the call centre once again, and the they told me that they will escalate the problem to the manager and that he/she will contact me during the day. Yesterday the 7th of February once again I contact the Call Centre again with the same problem that I am still waiting for my account to be sorted since November and the answer will escalate again, just to inform me that there is a back log of queries.