Xfinity On Demand $5.99 Coupon not working

I received a card that says Here's a happy holiday surprise. 'Enjoy a movie night on us: Take $5.99 off your next Xfinity On Demand movie rental or purchase. Or simply use it as a credit towards your xfinity bill. When I attempted to redeem I am asked to enter a 16 digit code and I have no idea where this code is. This is not a happy holiday surprise.