One of the Google’s amazing app messenger, default SMS app Messenger provides a unique option to add numbers to block list of Nougat. Here, are some options to try.

1. Firstly open the messenger app
2. Click the menu button on the top right corner.
3. Then go to list of blocked contacts.
4. Click in the menu add a number.
5. Type the number you want to block.

Also you can long-press the contact and add it to block list by tapping circular button at the top corner. You’ll be also notified of any spam reporting along with blocking the number.