Mtn can overcharge me and just ignore my inquiries

I have bean calling the MTN customer service line from the 20th of July and no joy regarding my overcharged account. MTN is charging me R800 per month for an A35 phone that was supposedly free on the contract that was signed at Menlyn MTN. Phone call after phone call no feedback. Lady " no sur you have to phone us to findout after 2 day" still no joy no feedback even if I phone them. The best thing is they will never let you speak to a manager. So I was suppose to upgrade all my lines but it seems like I will not be doing that with MTN as a loyal client for 10 plus years spending 4k per month minimum I feel disgusted by there poor service