If its seemingly from BT, forward as attachment to email@example.com, if firstname.lastname@example.org
Then delete the email
Even real-looking emails may have been spoofed
Never log in to an account via an email if you are unsure, instead go to the website to log in "manually" at bt.com. This avoids you being caught out by potentially clicking on links you do not know. This applies to all your accounts online, not just BT.
Check the sender email
Hover over the hyperlink (do not click) to check the original link url
If you suspect an email as being a scam it invariably is. If you have any doubt do not click on any links contained in the email. Log onto your MyBT account using your normal trusted route and you can view your bill there.