Incorrectly billed and nobody will actually resolve it!

A sales consultant phoned me to upgrade my contract. I did not upgrade but changed my data and voice plan. For some reason she changed my billing date and I was billed on the 1st as usual but then again on the 7th. I phoned to have this corrected, the call centre agent logged a call and said she would escalate it. I was promised a 2-3 day response. A week later, I had heard nothing and my outstanding amount was still double what it should have been. I called again, the agent this time said she could see the query that was logged. For some reason nothing had been done about it. I asked this agent to escalate it, which I was under the impression she had done. Now, with it being a new month, I have been billed yet AGAIN (3 times now since the start of March) and my service has been suspended.

I have been a very loyal contract holder for so many years I cannot even remember when it started... seriously considering ending it all!

Will somebody please sort this out now!?!