Terrible Customer Service

I have had a terrible experience with Mondo deals and MTN Morningside Jhb , my husband app**** for a cellphone through the website and upon delivery discovered that it was the wrong device that was delivered. This dates back to September 2021 . The device was returned the same day to the nearest MTN store , which was MTN Morningside Jhb , Emails was sent to Mondo to confirm that they have received the device and sim card back and to cancel the contract with MTN . This dates back to September last year to date nothing has happened . Customer care representative are not providing feedback with what the status is of the query meanwhile MTN is debiting the account with thousands of rands . Numerous trips to MTN Morningside Jhb to resolve the matter with no end in site. My husband who hold an account with MTN, He has made numerous trips to MTN Morningside has even opened a case of ***** and provided the store with a affidavit but this matter was then brushed off, The device that was returned to the MTN Morningside branch is still lost in transit , we were provide with reference numbers as proof that the device and sim card was returned to the MTN Morningside store , 5 months later. Nobody can provide answers as to where the device is. Mondo claims they are still waiting for RMA number to cancel device and sim . Surely the customer cannot be held liable and be charged monthly when there is proof that the device was handed in at the store.? Please can someone assist with finding a resolution to this nightmare.!!!