I'm not sure why support is telling you that you need to wait for a prompt, but that won't happen - as I said, progress is not linked to platform accounts.
You said that you added your Xbox account - by that you mean that you linked it to your current EA account, correct? In order to play Apex, your Xbox was connected to a different EA Account beforehand, otherwise you wouldn't have been able to play at all. Please find that account again and link the Xbox account back to it. Without that, you won't be able to play with the Xbox progression.