Xbox login EA account issue

Hello. Are you saying that you want to link a different Xbox gamertag to your EA Account? If so, that won't be possible as you can only link one Xbox gamertag to an EA Account in its lifetime. More information on linking accounts can be found here.

But I have already unlinked my old Xbox account and cannot log in on my current Xbox account

You will need to contact Xbox support for help with logging into your Xbox account.