Thank you for posting and welcome to the Community.
I'm sorry your BT Reward Card has been damaged. The Reward Cards are issued by Pure Card and you can contact them directly to request a replacement Card.
The contact details for Pure Card are -
Email - BT@Purecard.com
Telephone - 0344 879 1068, available from 9AM to 6PM Monday to Friday.
Post - BT Reward Card, Westside, London Road, Hemel Hempstead, Hertfordshire, HP3 9TD
You can find out more here - BT Reward Card