iPhone says wifi password is incorrect but it isn't

You have done all that you (or we) can do unless you want to change the name of the Wi-Fi network and password on the Xfinity router to see if that makes any difference.

It's looking like a Wi-Fi issue on the phone that will need attention at the Apple Store or authorized Apple service shop.

You can find a list of authorized service shops in your area using this link: Find Locations

Tap Settings > Wi-Fi

Tap Edit at the upper right of the screen

A list of networks to which your phone has connected in the past will appear

Look for the name of the Xfinity network and then tap on the blue "i" next to the name of the network

Tap Forget This Network

Power off the phone

Power off the Wi-Fi router

Wait a minute

Power up the Wi-Fi router

Power up the phone

Try to connect to the Xinfity network again

It its not working anywhere, then there's an issue with the Wifi receiver in the phone. You'll need to find a way to schedule an appointment at your Apple Store Genius Bar for evaluation and options.

Do you use a VPN on your iPhone? If you do, at a minimum turn it off, but preferably delete it altogether as VPN on iPhone is not necessary and can cause all sorts of issues.

If you don't use VPN, go to a neighbors house or a public location and see if you can use Wifi anywhere else.

If both Wi-Fi and Data are acting up, that is certainly a service needed situation with the phone.