Welcome to this user forum.
The email should have arrived by now if the order was eligible. What date did you place your order on?
14 days would be the 2nd January, but owing to the holiday period, it might have been delayed, also all of the orders need to close, and that can take a few days after installation.
You will be sent an email 14 days after your order closed. It will contain all of the information needed to claim along with a direct link to the BT Shop.
If the email has not arrived by the middle of next week, then post back here