Please Help me to cancel contract of router

Good day

Please help me to cancel contract with mtn and my story are as follows:

I bought contract router on the 28th June 2018 at mtn mall I the norh, when i arrived at home I tried to connect and it never connected, I phoned consultant who helped me and he advised me to call coverage department to check network which I called them and they say where I'm staying there is no network he advised me to return the router to the mtn shop and I returned the router on 2nd of July 2018 and they took it but the contract is still on and they debit order is always running in my account, remember I pay something I font have.

When I do follow up they say they gonna sent technical to check if there is network in my place and I also tell them that I'm no more looking for the router bcoz is already returned and now they say I used 40mb of data that's they won't cancel it. I never used any data.

So please help me to cancel that contract because I never used it but they are debiting me every month and they I must pay R1000 do that they can cancel it and I front have that money as I returned the router within 7 days.

When I called cancellation department they refer me back to the shop and if im in the shop they say i used 40mb ofdata, I just doing up and down and solution i get

Please please help me to cancel the contract of router because I can't keep something that don't benefit me.