Faulty device. Vodacom does not want to refund

Bought a device from vodacom in pavillion. Its a modem made by vodafone. I inserted my telkom sim card and it just does not want to stay connected. I returned to the store 3 days later to return it but vodacom refused. They said according to the CPA they dont have to take it back. The manager gave us attitude and even had a smirk on his face. Utterly disusted. Now I have a device that I cant use.