Cannot get a secondary signal

I get a sold 5 bars 4G and since I purchased 4 bars of 5G and my speeds were great 200-300.

Suddenly, 5g stopped - zero, nothing at all no connection - we swapped modems really tried everything, I’m only about 2 miles away, maybe less - same tower, the only tower in my area and I can see it so there are no obstructions.

Why did 5G stop, in my conversations with T-Mobile they cant seem to do anything because they are not the admins, I do get 50 megs or so with 4g so it’s acceptable, but not what it was for over a year…

Any suggestions would be greatly appreciated.