Unfair treatment

I took a month to month data package with them, wasn't happy tried canceling was told to return the router.. I went to the store to return and they refused it because "there's no Box" I made it clear agent didn't specify I need to keep the box only specified on the router was told "It's not in the T's and C's" when I asked why am i being penalized for something that's not on the terms and conditions couldn't answer me. Mondo and MTN is utterly ******* honestly. Now they wana debit me for the router theh don't wana take... Still in good condition no scratches or anything with their charger.. Only used it for two months