Royal Mail Group review: Sending a letter by end to end tracking and a signature on delivery

I posted a very important and personal letter with end to end tracking and signature on delivery.
I always use this Post Office and never had any problems with using this way of sending a letter.
The following is an extract from my receipt.
Posted 0n 15/10/2026 at 10.12am
Cost of posting letter tracked £5.45
The Post Office used to send Letter

Bishopdown
35 Barrington Road
Bishopdown
Salisbury
Wiltshire

Reference number
0213-74EE-026E-1592
Building Name or Number Postcode
Mill Stream Salisbury SP1 3SL

Delivery aim: 2-3 working days.
End to end tracking, with signature on delivery. Tracking at royalmail.com or Royal Mail app.

I checked daily on the Royal Mail tracking site using the tracking number but the response was unable to find, try again later.
I have check again today 21/10/2026 and I am still getting the same response. I have nothing to prove the letter in transit and I do not have the proof of delivery of the letter.
I am complaining because I have no proof of the tracking or the signature for delivery.
I therefore request a full refund of my payment for £5.45, Royal Mail have not supplied or carried out the end to end tracking and a signature on receipt of delivery.
I have no idea if the very important letter reach the destination Mill Stream Salisbury SP1 3SL