Help me with On Air Tv.

I need this company investigated asap. Last month I received a call from an agent selling a decoder contract...she explained that the subscription is on a 24 month contract basis and that the decoder will start working immediately. She also said there will be numerous channels playing and also there will be Wifi and also a cellphone sim card containing airtime worth 50rands would be sent every month which would be free. Decoder arrived as promised...guess what? It's not playing and the simcard has 0 airtime and I can't get help from On Air. I decided to cancel the deal and am told that I cannot cancel because I had an agreement!!! I have a problem with that...how can I be forced to pay for services that I'm not getting? I want them to take back their decoder...pls help me do that. PS...they have not deducted any money yet and I don't want them to.