MTN cancelation of contract

I got an additional contract with MTN on 25 October 2020 at their Southgate store . Only received the device on the 28th. I was unhappy with it and returned it to the store on the 29th. I requested for the contract to be canceled. I've been given the runaround since then, they canceled the contract on 17 December but charged me for the device which I returned and have a reference number for. I've since been charged and debited monthly for the contract that I requested cancelation for within their cooling period and have an outstanding of 16k for a device I don't even have. The consultants that are supposed to be dealing with the issue are not responding to my emails and don't even answer their phones. I've tried to get help from their customer service department and their Twitter account all in vain. Please assist.