Problem sorted.
You've got all the money you need you bonehead.

It's called unfair dismissal, and you can sue. Just so you know, I'm not one of these crazy people that walks around going, "i'll sue, i'll sue"

You actually have a legitimate case.

Firstly, you already have had the holiday and am sure you can trace when you booked the holiday and what not.
Therefore you would of booked it before you joined the company, otherwise you would of known they wouldn't let you have it, if you booked it after you joined.
Every company in the world now ask's if you have a holiday booked before they accept you, because they need to know your availability. Plus, regardless of what some shitty piece of paper says, if you are going to have a holiday, it would have to be authorised by a member of management or whatever, and a copy of your holiday booking will be kept behind in the human resources department.

So now.
:
1.We have proof, you had your holiday booked before you started work.

2.Around 99.9% of companies ask if you have any engagements in your first 3 months of work

3.If HR has a copy of your paperwork including your application, chances are it will have your details of requested holidays or even you informing the company when they are.

4.Your supervisor knew the situation and how far is he willing to take it? To court?

My honest advice would be to seek legal council in this matter,