Paying for Nothing.

I took an offer with Mondo and MTN and was instructed I have 10 days to return the device and cancel the contract if it did not meet my needs. On day 3 I sent an cancelation email and to make arrangements for device to be collected. After no response I phoned Mondo and was instructed by a call center agent to drop the device at my nearest MTN branch,which I did. I phoned Mondo on a weekly basis to follow up. Short story is they're warehouse can't find the laptop which means the contract with MTN can't be canceled and I am still paying for a device contract I no longer have. The last agent I spoke to said unfortunately until they locate that laptop I'll be paying. There is no feedback, no follow up. It's costing me money to phone them only to be given a new reference number and an empty promise that it is escalated and it will be resolved.