Joined BT in November, 2019, and I have been back and forth with BT, since January on this issue.
Was advised by a chat agent to contact email@example.com who referred the case to firstname.lastname@example.org but somehow, nothing seems to have been resolved.
Chat agent advised again to ask in the community.
What date did you place your order, and did you claim 14 days after your service was activated?
Also check that there was a reward card offered on the date you placed your order, by looking at the T&Cs.