Well as you are abroad, and only received one week notice, it is certainly not your fault. Maybe you should just apologise to the examiners explaining that you were abroad at the time, and were only given one weeks notice (or if you have their emails, just send them an email). I don't think the examiners would mind, would they?
You could also ask the secretary to explain the situation to them. If she knows she made a mistake, she may just admit it and apologise to them.