Is my score still there?

I once had an Xbox with the account (X) and played a game on CD.

I don't have the CD anymore, so I bought a new one - and also have a new Xbox, but the same Xbox account (X).

Is the save that I had before still there, even though it's a different Xbox and a new CD?

Yes

If your old console was connected to the Internet, the game saves are automatically saved in Microsoft's cloud.

If you log in with your old account again, the game status is available again.