There is a possibility that this is what happened:
First, tampons do not cost 10 dollars a pack. Not in a pharmacy and not even in an airport pharmacy.
The price MIGHT have been 198 Pesos ($198)
That's about 6.5 dollars
The store clerk charged your credit card, and the decimal did not work somehow, and your card got charged 1980 pesos ($1980) instead.
That would result in the US$62 approximately, the amount you were actually charged.
In this course of events, the clerk did not lie (she approximated the price to 10 US dollars - maybe she did not know the exchange rate, whatever) but I think 320 pesos for a pack of tampons is high.
Then, she charged the peso price and the decimal did not work, resulting in ten-fold charge.
Negligence? Intention? No one can say for sure. Either way, she should not have ripped or thrown away the receipt.
Also, she may have been right that it was not possible to issue credit, cardnet and visanet (local card processors) have problems with that kind of things, many times there are even problems releasing credit card holds (from hotels, car rentals), etc, and many times AUTHORIZATIONS pass as charges.
So she might have been right about her being unable to issue you a credit.
Senores, here, many people do not know how to process credit cards, on many occacions I have processed my card and completed transaction (swipingm, keying, etc.) myself at stores, gas stations, etc., because the staff was incompetent.