Billing-Incorrect package

I app**** for a 5GB plan on August 24th, 23rd, for R595, in accordance with the sales agent's phone conversation. After calling the customer service line this morning, I discovered that I had been paying an extra R200 on my account for the last three months. The agents put me on a higher plan with more costs, so I am asking for a refund for the extra money I didn't want to pay for those three months.