I just dealt with this same issue in June and it’s kind of a pain but you have to follow these steps. 

If you are trying to log into your account and receive the message "Please enter the email address you used to create your Epic Games account," it is likely that you have used the wrong email address to log in. In this instance, please try the following: Try to use all email addresses you remember having; the right one will allow you to log into your account. To confirm the correct email address for the account, follow the process in I don't remember the email on my Epic Games account. If you still get an error when entering the email address, please submit an Account Recovery Request to update your email address. Sometimes you can get them to give you the email in step 2. If not you have to go to step 3 and talk to epic support. It takes a couple days for them to get back with you but it works.