Bad Customer service

I upgraded my contact on September, than i took a laptop and a router. A month later the router broke dan took to an mtn store near, the lady told me they will send it to a warehouse but they cant give me a new router becouse their stock will be short and its not own by MTN its belongs to someone , she dan sad i should call MTN retention department where i took the contract . I ve been calling retention department for months now, spoke to 4 consultants giving me different stories up until today the router is not back. I pay my bill in time full amount, can u please advice me on wat to do becouse MTN wont even allow me to Cancel the whole thing