Mtn online data contracts (sim only)

I purchased an mtn data contact sim online on the 1st of July , I wasn't explained to me that the sim only works on a home router not portable routeror cellphone. the salesperson said if I'm not happy I can cancel withing 10 days.

Now I want to cancel or change the plan everyone I call on the MTN helpline give me excuses and direct me to someone else and they end up giving me this numbers ***, ***, ***, 083135 which doesn't go through at all. I am crossed because they were quick to call me for a contract and don't care about their clients concerns or complaints.