Send a change request (/help/change-request) and choose "I was charged twice for the same thing", with one of the receipt numbers and your e-mail.
If our records show a second charge of the same amount, within 72 hours, for something the first one already paid for, we refund the extra one straight away — and you keep what the first one paid for. If we can't see the second charge, or the two charges were for different things (Priority Review on two different applications, say), a person compares your statement with our records — a screenshot of your statement helps.
A pending authorisation that disappears from your statement in a few days isn't a second charge; if it's still there after a week, send the request.
Send a change request: billing mistakes our records prove are refunded automatically, and a person answers the rest within two business days.