i have echo reception what i can only describe as choppy blurred voice on iphone x

I have an iPhone X reception very poor compared to 6 scratchy cranky echo cuts in and out showed to Apple bought from Apple through att next went to Apple store when they found out purchased through att next program on their site at their store took back new phone they applewere going to give me and wanted to give me some service phone. They say they can’t replace with new normal boxed phone want to replace it with service phone not helpful phone is awful anyone else had this poor customer experience?