Billing discrepancies between what was agreed to and invoice

I am saddened that I am having to yet again I am forced to give a negative review and already considering cancelling the contract for the following reasons: 1)- The agent who vetted me for the contract, told me that I'd be paying R229+ pro rata as the first installment when my account is debited on the 7th of July 2020. I received the device on the 19th of June and it was not even active until the 22nd June, however when I check what my balances are, I see "unbilled charges" on the contract that exceeds by a very wide margin, the charges that the Mondo agent who took me through my application and myself agreed to.. In good faith, I promptly called the MTN department at Mondo, who told me to call MTN, who again told me to call Mondo and the back and a back and forth routine is being established. I think it's pretty shameful