That's odd. In that case just log on to your bt.com account and My BT and go from there.
I went to my my bt account and strangely is showed zero of the 2 licenses in use so I activated it checked and still showing about to expire then I tried the BUY option as you suggested this time I was taken to the BT site, I deactivated and then reactivated but again still showing that the subscription is about to deactivate.
Just checked again and it said expired I then clicked something I cannot remember what I think it was renew and it now says valid. I hope that is it now as I have spent hours on this over the last few days.
I assume we update on a regular basis and at some point the firewall will work, I gather this may be the start of December.
Have again downloaded BT McAfee and just get version 220.127.116.11 which is not compatible.
I am puzzled that a large organisation like BT is so behind on such an important issue as this.
I have been messing with this for 2 days and now have it up and running.
Initially when I downloaded it it was the old version.
But I did 2 updates and each time restarted the Mac and eventually it showed 18.104.22.168
I also had to follow the instructions given in an earlier post because one of the macfee items was not given full disk access in the privacy tab I think it was the one called fmpd.