When I tried to update my phone, it told me to sign in but when I tried to sign in, the account that is says it's there doesn't exist anymore so idk what to do

So I downloaded an update for my Iphone and it told me to sign in in the Activation Lock screen and so I tried. I tried to sign in but when I checked to see which email it was, the email didn't exist anymore😕. I tried logging in with the email I have now but it doesn't let me and now it says I've been logged out for security reasons and idk what to do. HELP PLEASE