overcharged account

18 months ago I took a Telkom mix with a Samsung s5 and my land line. My s5 account was supposed to be R350 per month but for the last 16 months I've been overcharged at R480 per month. I've called through several times to customer services and spoken to numerous consultants at the branch with no resolution to my problem...Every time I call through I get told that someone will get back to me. If you log into my account you will be able to see a number of reference numbers but nothing has been done to fix this problem...16 months into my contract. A manual discount was put in twice but this is really gone too far and I need some kind of explanation and solution.