Unauthorised costs on my account

I have a Cell C Router at home and on 23 June 2018 I contacted 140 and asked to load an additional 500MB data. The consultant advised me that they would need to increase my limit (which I requested to be only R50.00 when I took the contract). What she did not advise me on was that I need to contact Cell C again at the end of that month to decrease the limit back to R50.00. End of July, August I had a bill of approximately R200.00 more than what I was supposed to pay and this will continue till end of October due to subscription services, which they can not find on my account. I went into our Customer Care office to query the amount deducted from my account. The lady that assisted me, was absolutely great in her customer service, but the same can not be said about the people she contacted at the Head office. The lady that assisted said that if they assist with this type of request in store, they tell the customer that they need to come back in order to reduce the limit again, why can't the call centre not do this as well as the customer does not work for Cell C. She contacted head office and they just refuse to refund or credit my account with the additional costs that I did not authorise.

And I don't work for Cell C, so I think it is very unfair to lay the responsibility on the customer.

I have always defended Cell C when someone bad mouthed them as I have never had bad service from them, but now they force me to jump ship.