Hey TTonnex,
Sorry to hear your progress seems to have been reset. Usually when this happens, it's due to unlinking a platform or linking one to a different EA account.
Progress is stored on the EA account level, not on individual platforms like PlayStation, Xbox, Steam, etc. This means if you link your platform to a different EA account, you'll lose access to that progress and it will appear to have reset. Progress cannot be moved between different accounts.
I see you mentioned only playing on Steam in the past, however that would have been linked to a different EA account at the time. It is not possible to play Apex on Steam without linking to an EA account, so there is another EA account with that progress you're missing. You would need to try re-linking Steam to its original EA account to try restoring any progress.
For that it would be best to get back in touch with support so they can try to help recover the original account.