Sorry for your difficulties but happy you had a good tour. Your advice is well siad and very important. For travels to Europe (and, I suspect but do not know for sure) other continents as well, one needs a Debit (or ATM) card and one or more credit cards, either Visa or MasterCard. And at least one of the credit cards should provide the capability to withdraw funds from an ATM machine. Granted, the cost of cash withdrawals using a credit card is much greater than using a debit card, but it is a good backup.
You did not say why you went on the trip without a debit card, but your story should be a signal to GCT to strengthen the "suggestions" in their literature. Clients should be warned even more emphatically that currency exchange is difficult and costly. Use of ATMs should be emphasized.
Thank you for bringing this important subject to the fore.