This article provides methods to stop unwanted texts on iPhone. These instructions apply to the iPhone's built-in Messages app and not to third-party tools.
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Once political groups or campaigns have your phone number, it’s very difficult to stop unwanted political text messages. That’s because organizations share their supporters’ numbers with each other (or even sell them). The best you can do is opt out of these text messages when you have them removed from a group or campaign list. However, this option won’t stop others from having your number.
Most of these texts tell you at the end of the message how to stop receiving them. The most common responses to stop unwanted political texts are Stop, Opt-Out, Unsubscribe, Cancel or Quit.
Reply to the message with the suggested option. If there is none, Stop is the best option. You should then unsubscribe.