When a user sends you an invitation to a new game, you will have the possibility to reject it if you don't wish to play.
You will be able to see the new Classic games in the Games tab, located in the second option of the bottom bar of the screen, with the list icon. When you select the game that has been sent to you, a pop-up will appear where you can either reject or accept it.
Please note that if you reject a game before it starts, your game statistics will not be affected.