A mistake, accident and human error can be rectified with an apology when you are charged twice for one item at the checkout.
Being prescribed the wrong dose by a pharmacist could cause very serious health problems and I would make a formal complaint in writing to NHS England. PO Box 16738. Redditch. B97 9PT. If you are in Scotland, Wales, N Ireland you will need to send it to the relevant authority.
Wait until you have spoken to your surgery to clarify the prescription that was sent. You should have received a paper copy and if you didn't - put that in the complaint, too.