ORBI NBR750 5gh cannot be disabled

I have an ORBI NBR750. I need to force the router to use only the 2.4 GHz antennas by disabling the 5 GHz ones. Even though I’ve done this, I still see some connected devices listed as connected to the 5 GHz band. I turned off the two satellites, restarted the router, but nothing changed; my iPhone is still connected to the 5 GHz band instead of the 2.4 GHz band. Netgear support doesn’t seem to respond to products that are out of warranty. How do I fix this? Also, the system tells me there’s a firmware update available, but in reality, there isn’t one. Is it possible to have all these bugs?