Being charged for a laptop that was returned.

Incredibly frustrated with the call centres of MTN. I was sold a laptop by Mondo and was misled re. the contract price. I was then billed at a higher contract price. I took this up with Mondo and they did an investigation and found that i was misled and agreed that the laptop be returned to an mtn store and i would get a refund and not be charged a cancellation fee. The laptop was then returned months ago, however i am still be charged for it and have not been refunded. I've called the call the MTN call centre multiple times to get this resolved. A ticket was opened and closed without anyone informing me of the outcome. When i called in about it they said they refuse to escalate to someone more senior. Instead they issued another ticket with the credit department that are now investigating. Such poor levels of owernship and customer service, i can't wait to shift network providers at the end of my current cellphone contract.