Having to tear the window cover off is what makes me suspect that the PIN is actually on the window as explained above.
When I encountered this I could see a faint image on the seemingly scratchable bit beneath but couldn't read it so scratched away only eventually I had scratched right through the paper. Then I found that the tear off strip, if placed on white paper, clearly revealed the PIN

Have you tried that? ...... Or like me did you rip the strip and bung it in the bin. I ended up with the bank explaining it all and having to send me a new PIN.

PS Woodstock tells me that with Nat West the strip has to be ripped off and the letter placed on white paper and the PIN appaers as if by magic.
PPS I hope it's not me you are huffy with ~ Only trying to help and am resisting all comment re your eyesight etc.