First, like KIA and others mentioned, report the incident to the Consumer Council if you are looking for any sort of compensation. I'm not sure you'll get much, but at least the stylist may receive some sort of warning.
Second, just let your hair be for a few days, if you really hate it, wear it up in a bun. Use a very moisturizing shampoo and deep conditioner to try and help the damage, especially if you will be having it re-dyed soon.
Finally, go to a reputable salon to have the darker color chemically lifted out. Toni and Guy should know what they're doing. Paul Gerrard is also wonderful (although not cheap) and their stylists are all trained in the UK or Australia and have plenty of experience dealing with your hair type. They have at least two excellent colorists there. Try contacting a colorist (at a good salon you feel comfortable with), explain the problem, maybe make an appointment for them to see your hair and they can recommend a solution from there.
Oh, and don't just walk into any more salons in HK. Get a recommendation or find someone trained in the UK, somewhere else in Europe, US, Australia, etc. Many stylists here do not have much experience dealing with blonde hair types. Its not to say that they're bad stylists, but they just don't necessarily have a lot of practice with blonde hair.