To stop receiving marketing messages from Supercell, open the Supercell ID menu from the in-game Settings. Then follow the steps below:
Tap the gear icon.
Go to the subscriptions section.
Tap the toggle next to ‘Receive news and updates’.
Once the toggle is gray, you will no longer receive messages from Supercell ID.
If you wish to receive news in the future, you can always follow these steps again and set the toggle back to green.