Are you using the app or browser version of the game?
If browser, i am wondering if you are actually logged on to the correct server. This forum is for the US server, so if you click "to the game" at the top you are likely to reach the US server, which may be where you began your BA city, but not your original world. EDIT - actually, since i am based in the UK, even from the US forum i am redirected to the EN (English International) server, not the US one)
check the web address when your city page is open
does it read for example us12.forgeofempires.com or en7.forgeofempires.com ?
on the mobile app it is impossible to see which server and world you are in from the city screen (which btw I personally find VERY annoying and un-user-friendly!)
you need to log out of your city from the setting menu, and see which flag is selected. you can then change the server, and pick which world you think your missing city might be in.
if none of this helps, contact support from the city you can access - they will be able to check if your other world is at least on the same server or not.