I also have a problem with scam and spam emails every day on my primary BT email address asking for responses on links or to unsubscribe, I know these are dodgy links so wish to change my primary address, my sub addresses are fine and wish to keep them.
BT no longer use a Primary email address or sub addresses. Each BT Broadband account has eleven email accounts that you can use and if you decide you can "gift" them to other people as per the second link I have posted.
You just need to stop using your email account and delete it.
You will need to remember and notify all your contacts about your new email address and also change your contact email address within your MyBT so that any emails that BT use to contact you reach the correct email address.