Sample email to a shop about an unapproved charge

Use this as a starting point. Keep it short and factual.

Subject: Invoice question, repair order #[number], [date]
Hello [Shop manager name],
On [date] I approved repair order #[number] for [brief description]
with a written estimate of $[approved amount].
The final invoice was $[billed amount]. It includes [item], which I did
not approve and was not told about before the work was done.
I am asking you to remove the unapproved charge of $[amount] and refund
it to my card within 14 days.
Attached are copies of the approved estimate and the final invoice.
Thank you,
[Your name]
[Phone number]