Not sure what's going on but here are the details again from MasterCard's website:
Buy 2 cinema tickets with your MasterCard and get 2 more!
We are giving everyone that buys 2 Cineworld tickets between 1st September and 31st October 2008 two more. All you need to do to take advantage of this great offer, is make sure you keep the receipt from your local Cineworld cinema when you buy a minimum of two tickets. Send your receipt with the completed application form below and a stamped, self addressed envelope to:
MasterCard Cineworld Cinema Promotion
PO Box 123
It couldn't be simpler... We will then send you two additional Cineworld vouchers each one valid for one free entry to any film at any time from Monday to Thursday until 12th December.
Your application must reach us on or before the 7th November 2008.