Thank you all for your advice.
As suggested, I put the phone in diagnostic mode but the Apple symbol didn't appear. The screen went black.
I plugged the phone in to the computer and iTunes said it had to finish being in diagnostic phase before anything could be done. I waited two hours, still couldn't turn the phone on, but could now start to restore the phone. That took another two hours as the download was 8.66gb and it kept dropping out.
The phone is now restored. There is still only the smallest line of wifi strength. I haven't made or received a phone call yet.
This iPhone 16e is two weeks old. It replaced an Oppo phone that had no reception issues.