Why do you even read those ads? The fine print always state they are for new customers only. Just shread them up and recycle.
They will keep sticking it to you as a customer, new or not. 3-4 years with them and last time I switched plans it came with free Showtime for year or two. Didn't ask for it or ever watch it. Told me it was up in December. No problem, could care less. Just got my bill and charged me 9.98 for something I didn't ever ask for or authorize.