If it helps, you should be able to get a preview from Google of the email address used to create the listing- just go to business.google.com/manage, add a new location, and when the screen appears that allows you to fill in the business information, start typing the name of your business until the auto-fill offers you the listing you're trying to get access to (see screenshot here: http://prntscr.com/g11erq). If the listing you're trying to get to doesn't appear in the autofill, type in the name of the business and then the city it's located in, all in the business name line; that usually brings it up for me. Once you have the correct auto fill and click "Continue" at the bottom of that window, GMB should give you the first two letters of the correct email address to log in with.
Hopefully, that helps you figure it out! Goodluck!