IPhone 11Pro changed ringtone on its own

Howdy Wflawrence,

Thanks for using the Apple Support Communities! I understand that even though you have a specific tone set your iPhone will not play the correct one. Let’s take a look and see what we can do. I'm happy to help!

Let's first take a look at this article that I was able to gather.

Select ringtones and vibrations on iPhone

"Change the alert tones and vibrations"

1. Go to Settings > Sounds & Haptics > Ringtone (on an iPhone with system haptics) or Settings > Sounds > Ringtone (on other iPhone models).
2. Make sure the correct ringtone is set.

"Assign a different ringtone to a contact"

1. Open the Contacts app.
2. Select a contact, tap Edit, tap Ringtone, then choose a ringtone.

Please respond back if you continue to have any issues with the follow up information. Are these specific contacts that have the wrong ringtone or are they system tones that are incorrect?

Best regards!