iphone 12 call quality

(2) iPhone 12's on ATT having call quality problems that weren't there 3months ago. Calls are almost undiscernible. Retrieving voicemails are almost indiscernible. Genius bar says nothing wrong with phone. ATT advanced tech support sent new SIM card and made network adjustments on my phone. Same result. Wife's phone has eSIM and same problem. My phone has been wiped and new software installed not recovered.

Using iPhone field signal check, unless I am within a 150yds of a tower my LTE or 5G signal strength never goes below -100db. Within 100yds I can get -86db. Data rates are slower than US Mail at 2.84mbps/0.05mbps. All measurements with case off.

Many others in my area complain of increase in bad call quality with both ATT and Verizon.

So are all the recent updates on the phones the problem? Carriers problems? Hackers causing slow down? Too many phones on each tower?