Internet & Cellular speed issue

I have had the home internet router now for over 1 year with great speeds until the turn of the new year.  I noticed it getting slower and just paid attention over time.  After getting to the point of not able able to stream or game it became apparent my cellular signal was also doing the same thing.  I finally called *611, gone through 3 reps that all determined something about the tower isn't right.  The tower is only 1.5 miles from my house and yes, I live in Alabama where there are hills, divots, dips and forestry, but even with all of that I received around 300 mbps at first.  It remained at that speed until it began to slow down to nothing.  My latest speed test was around 1….maybe 1.5…..mbps.  I've been told there was an overheated component on the tower that has now been replaced and received a replacement model of the router I had.  I couldn't even connect to the new router and took it to my local T-Mobile store and they were gracious enough to just take it and gave me a newer model.  I set it up about an hour ago and I still only receive around 1 maybe 1.5 mbps.  All 4 of our cell phones (all 5G compatible) are showing the same speed on the network with wi-fi turned off.  It's both our cellular signal and my gateway.  Something isn't right and Tech Support can't figure it out I guess.  I'm so frustrated and should be able to get this resolved and quit paying for nothingness.  

Anyone have a clue where I should go next?