I see allot of people saying this, thinking they've lost their account. Here's the fix, if you still have issues, I'll gladly post the rest of the info listed from EA.
If you’ve linked your account to Game Center or Google Play, your game information is saved and secure.
Sometimes, upgrading apps or your device's operating system can sign you out of your Game Center or Google Play account without telling you.
If this happens, when you log into Galaxy of Heroes you may think that your account is missing or that your saved information has been lost.
If your game is linked to Game Center or Google Play, you can recover it, your progress, and your units by logging back into your account.
Google Play accounts (Android):
Open the Settings menu in-game by tapping on the Gear icon in the top left of the cantina screen.
If you’re logged out, you’ll see a button that says Sign into Google Play.
Tap that button and you’ll be asked to confirm that you’re logging out of the current account.
Tap Confirm and your game will reload.
After the reload, you’ll be asked if you want to Play as Guest or Sign into Google Play.
Tap Sign in to Google Play and once you have logged in, your linked game will load.
Game Center accounts (iOS):
On your device, tap Settings then Game Center.
Sign in with your Apple ID and password.
If you’re already logged in to a different Apple ID on your device, tap that Apple ID, then tap Sign Out
Tap Sign In, then enter your Apple ID and password that was linked with your game
Close and restart the game and it will load up your linked account.
See this Apple help article for more information about signing in with different Apple ID’s.
