Heya DeadPhoenix196
Data/Progress attained by playing games is stored directly on the EA Account.
This means that if you play on a platform account (e.g. Steam, Xbox) that the progress you make whilst playing on that platform, will be stored under the EA Account and not the platform account.
This means that if you relink your Xbox account, that it wouldn't bring over any progress, as this would be stored on the EA Account it was originally connected to.
If I'm correct, the data should still be stored under the EA Account your Xbox account was originally linked to. You can access your old progress by making use of that EA Account.
There is no way to transfer data from one EA Account to another, so the only place where you can access that progress is on that EA Account that your Xbox account was originally linked to.
This can be done by logging in with that EA Account on PC, or by using a platform account connected to that EA Account.