You either need to be in the final or last month of a pass to add a new pass. Just copy and paste the following code for 3 Months of sky cinema for £1.66 per month. You need to cancel after the last payment of £1.66 on the final month otherwise will automatically roll over onto the normal plan of £9.99 per month.
Code is as follows: NOW4AQ66B3DWDE
(might be account specific) This is the code I got from the Galaxy Deal Browser Link from My Galaxy) Apologies if it is!