I've no official capacity with BT but I am currently struggling to get a reward card and my 3-month limit for claiming runs out on 5th June, which should be interesting, and I noticed no-one has replied to your post yet.
As I'm on my 3rd 30-day wait I've used/explored many of the enquiry/contact pages myself. What kind of message are you getting back when you try to use the instructions. Are you actually getting to a page to enter your claim details?
If you have any difficulty claiming you can get in touch with the rewards card team here.
Post back and let us know how you get on.