you can definitely fast track regardless of your situation! The helpline staff are clearly recruited to screen calls and put people forward for call backs. It’s not helpful but what I know for sure is that you are eligible to fast track as long as you are within 14 days of your departure date. I don’t believe we have the option of the same day service (premium) but we definitely do for the fast track.
I think this entire forum has more knowledge than the helpline. Good luck, all!