iPhone X, weak Signal, breaks up, drops WiFi

I got the iPhone X and have had constant problems with weak signal, dropping of WiFi in areas that I never had problems before. My wife kept her iPhone 6 Plus S and she can be sitting next to me and people say I am breaking up and they can't understand me. They call her phone and she is crystal clear.

Complained to T-Moble and they did their checks from their end and then had me go get a new sim card to make sure it was not them.

Finally went in to Apple Store and they did their checks and decided to replace the phone with a new one. Did not work, same problems.

Contacted Apple via phone and young lady had me wipe my phone and download new software, and set it up as new phone without down loading old setting and backup. There is no change, phone still breaks up, when making phone calls and drops WiFi.

How can I get rid of this new phone and go back to an earlier version??????

Spent almost 1500 dollars thinking I was getting the best and greatest, but having problem doing the simplest thing, calling people on a cell phone.

Answers??????????