Mondo Poor Service

I took a contract with Mondo MTN, but then they delivered me Wrong product(Router & Sim) and i called them they told me to return the Router & Sim to MTN SHOP so that they can Cancel the contract,this happened in April"19 but even now (August) the contract is not canceled because MTN is deducting my Money for something that I don't have. Everytime when i call Mondo they telling me that MTN did not give them a Contract Cancellation letter. I am not happy with how they treating me???? and no One bothers to keep me updated. ***