Onair did false advertising and they were not honest with me

The agent from onair contacted me and told me that they are facing out old DSTV decoder and they are now providing us with free wireless devices which a more advanced, I provided then with my address to deliver the device .only to discover that the agent was misrepresenting and not honest. I thought the device is for free but now she made me agree to a contract of the device package by false advertising. I enquired to them to cancel the contract ,they told me i cannot cancel ,only option is to pay off the account. And i haven't even activated the device or either opened it . Am afraid if i miss the subscription it will affect my credit score.