There are a few possible reasons for this:
1. You could be subscribed to a service that sends out duplicate texts. To fix this, you can unsubscribe from the service or contact the company to ask why you are receiving duplicate texts.
2. Your phone could be configured to send out duplicate texts. To fix this, you can go into your phone's settings and turn off the duplicate text feature.
3. You could be accidentally sending out duplicate texts yourself. To fix this, you can check your text history to see if you are sending out duplicate texts and stop doing it.