Comcast like many entertainment providers (AT&T, DISH Network, Direct TV, U-Verse etc..) from time to time have their contracts with various providers terminate and be up for renewal and then it's a tug a war between the entertainment cable provider and the channel supplier. This page (linked to) is the Comcast Contract Renewal page that shows what channels are about to expire and in need of renewal. As for the Florence, Alabama Comcast channel lineup ... no channel 11 or 12 Click on that link. Also some cable and entertainment providers move channels around but usually put a disclaimer on the old channel pointing to the new channel but then that might be too customer friendly a practice for Comcast.
I had Comcast and Direct TV as well as AT&T U-Verse but I now have, and totally enjoy better, Dish Network. As for now I don't see me leaving Dish even after the contract is up. I actually paid AT&T/Direct-TV a fee to leave early and it's the best move I ever made as there is no comparison between Dish and Direct-TV, Dish is by far and away better in features and price and unlike Direct TV & AT&T Dish's price remains constant and what they tell you it will be. AT&T/Direct-TV totally lies to you and their employees don't know what one hand tells the other. I'll never go back to AT&T for anything, at least unless I have to for lack of any other service. Right now though DISH is in talks to renew Cinemax and as of now neither Dish Network nor Cinemax is moving on Price. Dish on what they will pay and Cinemax on what they want to charge. Back to your question ...
Another linked page I followed had a list of Comcast/Xfinity channels and it did have a Channel 11 & 12 and I'll post that below to see if it jogs a memory.
1 XFINITY ON DEMAND 2 WLBT (NBC)
4 WAPT (ABC)
7 WMPN (PBS)
8 WRBJ (TBN)
11 WUFX (MYNETWORKTV)
12 THE WEATHER CHANNEL
13 WJTV (CBS)
14 W23BC (JACKSON STATE)
17 WWJX (MYFAMILYTV)
18 PUBLIC/EDUCATIONAL ACCESS 19 EDUCATIONAL ACCESS
20 PEARL CITY ACCESS CHANNEL 81 C-SPAN2
89 EVINE LIVE
98 NOAA/BULLETIN BOARD/LEASED