You can do it all on line;
Go to, mailonline.co.uk/rewards
then log in, if you use the numbers I assume your registered.
To the left of the green box where you enter your numbers there is a blue box, the last entry in this box is 'Missing unique number card'
Select this option and away you go, just tell them your card was missing and there's no charge.
Here endeth the lesson.
;o)