How do I stop Unknown Group messages?

Hi 76-79-83,

Welcome to Apple Support Communities. We understand that you're having an issue with leaving or deleting this group text message. We'd like to help.

From what you've shared, it looks like this message is being sent as an SMS text instead of an iMessage. If this was a group text, using iMessage, you would be able to leave that type of group. However, SMS is controlled by your wireless carrier. At this point, it would be helpful to reach out to them for assistance on how to stop messages in this group chat.

This resource can help you with the difference between the different type of messages used in the Messages app.

What is the difference between iMessage and SMS/MMS?

Learn why some of your message bubbles are blue or green.

You can use the Messages app on your iPhone, iPad, or iPod touch to send messages. Those messages are sent as iMessage or SMS/MMS. Learn more about the difference between the message types.

iMessage

iMessages are texts, photos, or videos that you send to another iPhone, iPad, iPod touch, or Mac over Wi-Fi or cellular-data networks. These messages are always encrypted and appear in blue text bubbles. To turn iMessage on or off, go to Settings > Messages.

SMS/MMS

If you aren’t using iMessage, you can use SMS/MMS. These messages are texts and photos that you send to other cell phones or another iPhone, iPad, or iPod touch. SMS/MMS messages aren't encrypted and appear in green text bubbles on your device.

To use SMS/MMS on an iPhone, you need a text-messaging plan. Contact your wireless carrier for more information. You can also set up your other Apple devices to send and receive messages from any Apple device.

If Wi-Fi is unavailable, iMessages will be sent over cellular data. Cellular data rates might apply.

Hope that helps.

Cheers!