Are you presently a BT Broadband customer or are you paying for your email through a BT Premium email account?
The first thing to try is turn your iPhone off and back on.
At this stage DO NOT change your password or delete the email account from your iPhone. There is obviously nothing wrong with your password if you can access your email account on other devices.
Was your email account set up on the same BT Broadband account as your husbands?
If neither of the above your email account may have been downgraded to a BTMail Basic account which can not be used with an email client.
See link
https://www.bt.com/help/email/bt-email-products
To check log onto your MyBT and go to "Your Products" then "Email, Manage" then look at what type is your email account is showing as.
