chalie2566, I figured out that the reference number you got for your passport should be used as PAN number on the TNT website, without the letters (POD or POX), just the digits. Then you can see the consignment number given to you and all shipping info.
I paid for tracked return of the old passport and now I can see that it will be delivered first, hopefully the same PAN number will then work when I need to track the new passport.