business above customer service

Took an mtn router contract from mondo in january and it came in february. Connected it and was told it will work within 36 to 48 hours and when it didn't went to the closest mtn,was told they cant help,called mondo and was told to return it which i did within 7 days.Was told to cancel the contract which i did now mtn is saying im owing R3700 for administration and they have put me to credit bureau. I have called mondo and they keep saying they putting in the request to have my name removed or cleared.