It's gone for me too, I have the digital starter package, so I can afford some decent TV, i.e. HBO and Showtime and now AMC says Not Authorized. Sucks cause I was looking forward to Breaking Bad. This came as a complete surprise to me as my TIVO is taping some old episodes but there is nothing to record. Now I have to wait for Netflix to pick it up after the season is over. This is getting ridiculous Comcast, should I just sign my check over to you so I can watch some TV worth watching once in a while? No wonder you're losing your customer base and have to give away Visa gift cards to replace your base but what happens when they cut the cord too? Exactly.
I contacted Comcast and sure enough AMC had been moved to the next highest tier. The customer service rep was very helpful and told me I could add it for 9.99 a month for a year instead of the normal rate of 19.99. Of course I said yes and now I can watch Breaking Bad. Thank you Comcast for the great customer service. I still think your pricing is to high but you get what you pay for.
Call Comcast, be polite (it isn't the fault of the person you are speaking to..they have no control over what happens) and POLITELY ask for a credit. They will give it to you if it is a reasonable amount.