How to Prevent Teen from Stopping Family Sharing

My teen is part of our family sharing group. I manage their screen time because we have had issues with them managing their own repeatedly. I am able to manage it remotely, and it has worked well for us. Since we got new phones, the option to "stop family sharing" appeared on my teen's phone despite my having screen time restrictions in place, including not allowing them to make account changes. I know I can set a screen time passcode on the teen's phone directly, but it works better all around if we have the flexibility for me to manage it remotely. This is a HUGE problem for our family. Has anyone gotten a resolution to something like this?