I have done these in the past years, and always received the $25 back. I did have to call and pushback on a couple over the years, they would deny them but a phone call and they straightened it out and sent the rebate. I remember one year Showtime gave a coupon for 12 free Digorono pizzas, man that was alot of frozen pizza to buy at the grocery store in one trip. I think another year it was ice cream. The past few years have been consistently $25, good once a year.
You can probably combine it with the showtime/starz buy one get one free, but may need another premium on the bill to look like the free one. Then again, you can always try, if one of the two pay you got nearly three months free of both.