Hey aiikzzs,
Progress is stored on the EA account level, not on individual platforms like PlayStation, Xbox, Steam, etc. This means if you unlink your platform from its EA account, you'll lose access to that progress. This isn't specific to cross progression and will be the case any time a platform is unlinked.
You can try re-linking the original Xbox account back to this EA account to see if the progress returns. If you've already re-linked the original accounts and that still hasn't returned however, unfortunately that would be permanently lost and isn't something we can manually recover.
If you haven't yet tried re-linking the accounts and run into any trouble with that, please feel free to reach back out to support or resume your prior case so they can take a look at helping get those re-linked, though they wouldn't be able to manually restore any content outside that process I'm afraid.