Billed twice double the amount!! Since March and can't be solved.

Ever since I finished my contract then I took a data contract of R100 my problems started with this service provider. My bill for May was triple what I owe so I opened a case as I was being billed twice a month, double the amount. Case was resolved as per the sms, but again next month same issue for July. Asking them to check what happened with the resolved case "no you were credited back the excessive amount but only for that month". That's pathetic problem solving I was mad asked her to reopen that case until a root cause is solved. She promised me a call back from the billing department but that never happened. Thereafter I follow up as there is no call back she then re-sends another email as a reminder and requesting a callback too, I told her that billing department never calls back but she assured me they will. Friday the 30th of July I get billed another R202 on top of the R800. I immediately call telkom at 15h44 agent asked me to hold the line she is investigating, after 19minutes of holding she hangs up on me. What worse service can you get ? I want to cancel everything with telkom and get my money back cause they are useless and very good at sucking money for an awful service.