I'm sorry to hear that you've been experiencing issues trying to connect some devices to the new service! I noticed in your post that you had mentioned, "The password that worked with the ATT router doesn’t work.". I think that's the cause of confusion here.
The new service should have been installed with a new router, either a SmartRG (black box), or an Eero Mesh Router (White box) and it should have it's own brand new password to use. For the SmartRG router, the default WiFi password should be located on the label on the back of the device. For the Eero, you'll want to log into the Eero app to check what the password was created as.
Once you've found the password, try entering that for the printer and TV, then it should connect normally.
If not, please let us know so we can troubleshoot further.