In the United States, The Federal Trade Commission is the one to file complaints; https://www.ftc.gov/faq/consumer-protection/submit-consumer-complaint-ftc
I encourage every disgrundled customer to do this.
I'm eligible for an upgrade in September. I emailed Samsung. I got the old song and dance that in order to keep their stuff current, they have to take some features away. In other words, they're not planning on putting it back the way it was. Their "fix" of putting it in the settings on the messages thread was all they're planning on doing. And, I've been to look at other phones. Guess what? The pixel and the lg I looked at does the same thing as Samsung. The ONLY phone I've found that still let's you attach a notification tone to a contact is Iphone! I've been using Android since my first cell phone. I'm really thinking of going to Iphone now. I'm seriously weighing all my options. If any one can find a different phone that works on Sprint, I'm real interested! I love Android, but taking away that feature is a deal breaker for me.
My understanding is that LG still has it, but I want to stop into a store and test this myself. I like their phones and really dont want to go back to apple as I left specifically because of the headphone jack removal, but this feature is far more important to me.
I tried the lg ones at Best But. It wasn't on any of them that they're currently selling.
I looked at a coworkers LG the other day. It had the "Custom Text Tone" setting in the contact file when I checked it.