Sky Box Office Offer - shoddy customer service

Email sent today to Sky Customer Service

Sky sent me a letter entitled "Advance Notice Of Changes To Your Sky Subscription Service"

In it, Sky offered me a "Free Sky Box Office Movie"  To claim it, I had to register at a specific web address before 10-August.  When I did so this evening - 09-Aug - the web site said that the offer was unavailable.

So, I phoned the number on the letter - 08448 422450.  The lady to whom I spoke told me that I wasn't eligible for the offer because I had previously had Sky Movies on my tariff.

So, why did Sky send me a letter telling me that I was eligible for an offer then tell me that that was not in fact true? 

Why did the lady to whom I spoke tell me that it was impossible to provide feedback to Sky's marketing department?

Isn't this lying on Sky's part?  Offering me a service then saying that I couldn't have it?

regards,
/alan