Does your card has a CHIP?
Did the manager ask you to enter twice??
Of course there are places like Loblaw, and if you buy grocery there and the amount is less than 100 dollars, you just tap the card reader and then you get your receipt print out.
If the amount of both transactions are the same, and happened to be charged the same time, you have ground to report this to your credit card company, you file a dispute to the second transaction, your credit card company should give you a reference number for your case, and probably told you when you receive your statement, you don't have to pay for the second transaction.