Uninitiated group conversation with unknown contacts

There could be a lot of reasons this happened. By far the most likely reason is someone trying to scam you. If you need help identifying wether or not the message is a scam, refer to the article linked below.

Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams

Also look at these threads:

discussions.apple.com/thread/256035805?sortBy=rank

https://discussions.apple.com/thread/255711296?answerId=261484181

If you want, you can reply to this post and share a screenshot of the message you received. Make sure to cover any phone numbers or sensitive information. (Example below)

Have a good week!

If it indeed is a scam, based on what I told you, delete and report spam.