Dropping calls

We just got new iphone 8s through at&t three days ago and my fiance is having major problems with calls getting dropped.  He says he has full bars for service but he can't hold a conversation without it dropping the calls. My phone's touchscreen has been acting up.  I try clicking on something and my phone is froze and it won't register that I'm trying to click.  These are expensive and BRAND new phone.... so we would appreciate it if they worked properly...

Thank you.