Recurring suspicious incorrect billing

Since the 27th December there’s an additional amount being added to my account, I’ve called 5 times asking for this matter to be resolved, the amount gets reversed and billed again after 5 days and I get disconnected. I’ve gotten to extent where I have deleted the app from my phone because every time I call the call center agent comes up wit the story that this incorrect service may have been added on the self service. I no longer have the self service now but I’m billed again for something I don’t know. I’ve never experienced a company that is so big with a poorly managed billing system. On 4th January I spent an hour trying to resolve this problem, again on the 16th I spent 3 hours, my entire morning on the phone only to have this reversed and added again. Today I’m disconnected.