Incorrect Instalment and refund

I'm extremely disappointed in Telkom and it's staff members. I have been trying to resolve one issue for the past 2 with no clear resolution. My family and I have had a relationship with Telkom for almost 10 years now and I see they don't value the relationship anymore. Telkom keeps deducting the wrong incorrect instalment. I request that they cancel my contract and I will buy a cell phone cash. Their store keeps telling me my issue is resolved however the bill does not change. I also want a refund for the amounts deducted after submitting my request.