unhappy customer Mtn was the best but now the worst

i have a data contract with Mtn for years and never had issues until i decided to get a home router with them. the 1st 3 days i had it and it was not stable at all so before the 7 days i had called to cancel and went to a Mtn store to return it but i was told because i got the contract online they cannot take it back, i must arrange with Mtn to send a courier to collect it so i did that, Dsv collected and i got no slip or reference. a few days later i called and they said they waiting for the router then only they can cancel, long story short its 2 months now i have no router but i am paying for it 2 months already. N i have no idea how to fix this issue i have called so many times now im told to go to the store and ask them to call dsv to find out the reference number when they collected from me. shouldnt it be them that should call, i am taking time of work to call and go to the store when its there mess up. i am giving up now and thinking of cancelling both contracts with Mtn and stop my debit order completely i cannot be paying monthly for something the can check on there side its not in use.