Telkom mobile incorrect billing

I have taken out an account with Telkom mobile. They billed me incorrectly from the start of my contract and I have logged multiple cases over the last 6 months and been at the telkom shop multiple times. Every time billing department close the case without reason. Seems like Telkom doesn't understand how a contract works. I'm very disappointed at the billings department for not helping clients. I think I should take legal action because they are *****ing my money.