This is not a concert it is a game. I have never paid for a game that I wasn't able to play. I paid, i.e. credit card was charged two days ago. I have paid for a product I can't use.
Can't use "yet".
Just as you can't use a concert ticket the moment you buy it (or perhaps even two days later). It's called a similie.
You have purchased a product with a clear release date of the 19/20th (timezone/country depending).
If after the 20th of December you still have access issues, contact Customer Support.
If you have any confirmation you have been granted early access, but still can't access the game - also contact Customer Support.