Hi
They have an email address:
chadabangkok@gmail.com
You could try sending them an email and explaining the situation to them in simple English. If they are a hostel in Khao San Rd then someone there will speak/read basic English, as the clientele are almost entirely (young) foreigners.
Also, they also have 2 phone numbers on the website. Try both. Be sure you are dialling the number correctly (I think you have to drop the number in brackets dialling from abroad?) - it could be that you are dialling a wrong number and getting a random Thai person! (I have done this before :|)
Tel:
66 + (2) 629 0211
66 + (84) 434 7950
Good luck!
Steve