Trying to login in to BT email App, as it’s the only access I have to BT email. So BT send me a passcode to my BT email account. What is this meant to achieve except I cannot access my emails
BT send the email passcode to the recovery email address or text number they have on record in your profile under "Contact Details" in your MyBT.
If you did not populate that with an alternative email address or a text or phone number then most likely the default is to send it to an email address that is on record.
You could try using a browser with your correct log on details.