i had a similar issue a few years ago with a curtis sx frame i bought off some kid on the southerndownhill forum. nothing turned up for a few weeks and the guy was insisting he'd sent it all ok, giving me a dodgy tracking number which didn't work so i was getting a bit worried i'd been scammed. i then tried the local post office depot and asked if they had anything for my address as i was expecting an urgent parcel, after about 20mins looking they found it in the backroom! didn't have any calling cards or attempts of delivery as far as i could tell, it turned out he'd cheapskated and sent it standard parcels instead of first class/recorded (which we'd agreed) so that's why i couldn't track it! 😯
may not help too much but worth a visit to your local depot/collection centre to check?