Unlike @louisdi, not that I see any fault in his reply or approach --in general I find his troubleshooting to be very good and think he can find issues when lots of others can’t, just the same I am inclined to focus on finding out whether this is a coverage issue or not but I have a question that may confirm or eliminate it. The cell signal strength indicator triangle up in the notification bar at the top of your screen – does it have a tiny ‘x’ in the bottom right corner when you can’t update maps or send a text? If so that means you can’t get a data connection even if you have lots of bars of signal strength showing. In contrast when you DO have a data connection there would likely be two small triangles-- one pointing up and one pointing down flashing on and off on the right side (Upright bar) of the signal strength ‘meter’; those would indicate data is flowing upstream or downstream when the triangle is “on”. This isn’t an instant diagnosis i.e. you will have to watch any time you are doing an activity that requires data, like fetching email, sending an MMS (a plain text with an emoji in it or that is over 160 letters (including spaces and punctuation marks) will be treated as an MMS or picture text and will require a data connection. Short, plain, text messages can go over the cell voice connection. Besides being tedious and technical when you may prefer to be relaxed and casual these little things will let you know where you do and don’t have data available and eventually you will know where the data dead spots are. A good long term process; not a quick fix.
Hope this leads you to a fix even though it isn’t one on its own.