If you are still having this issue, we will need more information in order to better assist you. Do you have signal? This could be an error associated with wi-fi calling. Do you have wi-fi calling activated?
Its not just youre phone, it must be on the`ir end. my phone and 3 of my friends have the same problem and there are alot of other people posting network not avalible on android.com. it happened about 12 am wednesday morning. my phone has 4 bars but the 4g icon is missing.