As you are on BT Business broadband I assume you have a BT phone line. If so, you should be using the number in that checker, not your address. (All numbers if you have more than one line). As recommended on the checker screens.
There is a small chance of the address checker being wrong, and quite a high possibility of the postcode one also being wrong.
Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. Sync 54999/14466Kbps @ 600m. BQMs - IPv4