Carphone Warehouse trade ins

I've purchased a pixel 7 pro from Carphone Warehouse online, including a trade in. I have had confirmation email reply of the trade in submission, with a reference. The email stated that I would receive a return envelope to send in the phone within 3 days, but nothing received over a week later. I have chased via email, with no joy.

Could I simply take the phone to my local store, along with the reference details, and hand it in there instead? Does anyone have experience of doing that themselves?

Not at all confident of getting the £15 + £150 bonus as it stands!