@serhatvilla7 There is way to link the account in these cases, is via the guest account. First you need disconnect the Game Center, join in iOS settings, Game Center and be sure any account is connected. Then open the game in the guest account. If there is not any account there, you will see a button in the top left corner ("Have an account?"). Press there, then press on "Link a device" and put your Facebook data. Previously is needed connect to Facebook in the SWGoH settings of your Android device, on Connect, Facebook and put your data. If you have some account in the guest account you need replace it, the account must be at least level 6 to unlock the Facebook connect function in the game settings. After it write "DELETE" and your iOS guest account will be replaced. Now is needed use some Apple ID to connect to the Game Center, some account which never played the game, if you already started the game and your are level 3, level 6 or more will not be possible replace the account if you already linked it to some other Game Center account, if is the first time then yes is possible replace existing accounts. When you use a new account will appear a message asking "Continue game" or "Start a new game". You need press on "Continue game" and the guest account will automatically be linked to the Game Center.
When the accounts already are linked in some platform is not possible do a link to the same platform if is not done via the guest account, usually appears a message that says it, in this case appeared a different message, I don't know why, maybe on iOS not appears the same message that sometimes I see on Google Play, but if you try via the guest account it should work, because I did it several times to link a Google Play mail to a new Google Play mail.