95% of a conversation has nothing to do with the actual words used within. It all comes down to tone and body language. (One of the biggest reasons why I loathe the telephone and refuse, point-blank, to text. I do email, but I'm very good at getting my point across just with words, thanks to repeated editing.)
Personally, I wouldn't bother with sending a letter--but I'm just a lazy so-and-so, and would rather just take my business elsewhere. If it's a Tim's (and I'm only assuming this based on the rest of the thread) you can't throw a rock without hitting one in Ontario, so I'd just go to another one in future.
I'm sorry you had to go through this, Knitterly. I hope you're feeling better now. (If you've been on cold meds, you must have been ill. Again, I'm assuming.)