It may be there is something causing interference with the data signals.  I have the same issue when I am at home, but when I am out and about, I have 5g data. Sometimes it glitches when I am at work also. 

Wow, something is seriously wrong there. How is the reception in your area? What happens if you try your sim in another phone?

I live in an apartment building so it must be some of the materials used in the building.  When I go outside,  waiting for the bus, or even waiting by the front doors of my building I can get 5g. My unit faces the house next to my building, so there may be some inference also.  It also depends on time of day.  Later at night,  or early morning,  I get 5g. I have no issues using wifi at home. And at work, I work in a big box store,  so depending where I am in the building,  there is some inference from the building materials