First let's see if your WiFi is really working. Set the phone to Plane Mode. Now turn on WiFi only. Do you have Internet connection then? Do you still see the 4G icon? If not, then turn off Plane mode. Is 4G still on? If it is, then there might be a setting in your phone for mixing data modes. I know that that feature is present in newer Samsung phones to help boost downloads, but not sure if it's there (or where) on the V10. If it is, it should be sAdvanced WiFi settings or near the WiFi settings.