I agree with dx. We normally encourage people not to waffle, but your letter needs expanding on and some more detail of what happened on the day, I would say.
We also suggest buying a monthly or longer season ticket to show good faith, if you're a regular traveller.
Escalate to CEO level https://www.ceoemail.com/s.php?id=ceo-9152
And get back to the Waitrose branch manager to say you're going to return the goods you bought as you weren't told about this £100 surcharge.
Plus complete the sticky, it's difficult to resolve a case if we don't know what happened.
Don't touch them owe me £500 since January 2019 make excuse after excuse. Seem they always have software problems sending money out. Keep saying they will call back or email nothing been chasing it now for 6 mths the phone staff always have the same banter we will chase it up and get back to you then nothing!