There is absolutely no risk that this would happen if you call and report your card as stolen. None. Now, if you've already had a charge authorized, then yes,

There is absolutely no risk that this would happen if you call and report your card as stolen. None. Now, if you've already had a charge authorized, then yes, the issuers has to allow that charge to be captured, even if you cancelled the card in the interim. But your issuer can certainly tell you if there are any valid authorizations outstanding.