Reservation Problem

My sister made a mistake last Friday while she booked a hotel room in Prague, so I have been trying to fix it since then. However, I haven't been able to make contact with the hotel. I have sent them a few e-mails to them, but I haven't received any replies from them. I feel frustrated. Is it really going to be okay for sure as the hotel is not a typical hotel. It is a worldwide chain which means I don't need to worry about being cheated by them hotel. But, I just feel bad because It is stressful to deal with problems, especially if they lasts for a long time. I should have booked the room instead of my sister. It is so annoying that whenever I try to buy something online, my debit card is kind of seems to be blocked for some reason. Most of Korean banks require so many procedures to pass to the checks of whether I am the real card holder or not. I really think banks require too much at all times. Many Koreans have been complaining about this. The Funny thing is, Korean banks are very weak against hackers despite of the fact that they try not to be hacked. I think they should do something about that . In addition, I really hope I will get a reply from the hotel as soon as possible.