Regardless of when you worked, I find it seriously hard to understand why they are taking 50% tax off you? If an employee starts work, and does not complete a P46 or forward a P45, the code 0T should be used on a Week/Month 1 basis (which will be 20%)
Keep us updated, would love to know why they have done that.
This to be honest, I'm certain there is no such thing as emergency tax anymore where they take a higher percentage until they have sorted your code out.