cant get work email off my iphone after leaving job

I no longer work at my former company. The email is still on my phone. I have deleted the emails and it's no longer active but I keep getting the box popping up asking for Password for the Exchange Account. When I go to Settings/Mail/Accounts, I cannot delete the account. Everything is still there but faded out so I cannot toggle anything and no "delete account" at the bottom like my other accounts. I would really like to be able to stop that box from constantly popping up. Thanks.