Hello and thank you for the opportunity to assist you. My name is ***** ***** I will do my very best to answer your legal questions.
Yes, I'm sorry to say that the general rule is that when a contract is created, then it is final at that moment. In very limited circumstances that do not likely apply in this case, there is a 3 day window in which to cancel a contract ... this exception applies to door-to-door sales and mortgage. But just about every other type of contract, including cable TV, has no such rescission period, and the contract is final immediately.
However, the one possibility here that I see is that the cable company may have breached the contract if they guaranteed in writing that you will receive the channels in question without an antenna. If that is the case, then you could argue that the cable company breached the contract, and therefore, you are not obligated to honor it yourself. But you'd have to make that argument in court if the cable company won't release you voluntarily.
I am truly sorry that my answer may be bad news for you, but please understand that it would be unfair to you (and unprofessional of me) to provide you with anything less than an honest response. However, if your concerns were not satisfactorily addressed, then please let me know, and I will be happy to clarify my answer.