Deceived by Cell C's Customer Services

In March, I went to a Cell C store and requested to pay the total balance on my account for the duration of my contract upfront. The end date is in August. I carefully explained that I only want to settle the balance (pay upfront) and not terminate my benefits to which the agent confirmed that I would still receive my benefits for the duration of the contract. I payed the balance, with peace in mind that I no longer had to worry about monthly installments. In June, Cell C deducted an installment from my account. This alarmed me, so I contacted customer service. They informed me that the amount I payed was only for 3 months coverage and now installments will resume until August when the contract ends. I explained to the agent that this wasn't what I agreed to. She informed me that there's nothing that can be done. This was enough to upset me. I explained that we as customers do not know the inner workings of Cell C's services/processes. We rely on your agents/consultants to educate us and help us make informed decisions. I've been a loyal customer with Cell C for years and now on my third contract. Unless Cell C can resolve this issue, this will be my last contract.