In Nougat, you can now block those frequent agitators from calling or texting you ever again. In the Dialer app, tap the menu button, and then navigate to Settings > Call Blocking. From here, you can manually enter in any number you wish to block.
Nougat could help you rid of spam calls in the long run. Be sure to also enable the “Caller ID & spam” feature that’s available from the same Settings menu. Once it is turned on, Google will alert you if the number you are corresponding with has a spammy history.