Home router cancelation

Signed a contract with MTN and they gave me a router with no coverage at my area. I experienced zero coverage, I contacted them and they told me there’s no coverage I must return the home router at MTN store I did that within 2weeks. However, after a following the steps of cancellation they never actually cancelled the contract!!! Now I’m On arrears of R7000 for something I never even used!!! Not even 1 mega bytes usage! MTN please cancel the contract ASAP. Name and Surname: Precious Ngwenya Account number: BA*** Router number : *** Contact number: ***