For anyone else that comes across this frustrating issue.
When switching the FritzBox 7340 back to adsl from vdsl there is a bug where if it was originally setup with vdsl it will not work when changing the settings back.
So you can get all the settings right, and it shows the connection to the local exchange and the line rate etc, but the internet will not work at all.
Cycling the settings does not work.
The solution (from snap) is to Factory Reset the modem and start from scratch with ADSL settings.