I've been trying to figure this out for a while with no luck but maybe someone on here has had this sort of issue or knows how to fix it.
I have a verizon HTC 10 and the wifi works fine but whenever I turn it off it says "mobile data disconnected". I've tried resetting the network settings and removing/reinserting the sim card to no avail. According to a few google search results I looked at, you should be able to mess wit the access point names settings, but when I try to do that it says, "no SIM card found. Please insert a Sim card into the phone."
This doesn't make sense because I can call and text and stuff fine and it seems to work fine otherwise, which leads me to believe that the sim card is working. I even removed it and then reinserted it in the settings menu after I got the same message even tho the bar at the top obviously went from 4G to no connection back to 4G.
edit: I've had my phone for over a year now and up until ~1 month ago, the data and everything worked fine, until it just randomly stopped working recently.