Hello BillyJM.
Thanks for your first post and welcome to our Community.
Sorry to hear you are having an issue with your external bell not working after switching to our Fibre phone.
It may well be now you have been upgraded, the traditional landline is now de active and wont send a signal the external Bell.
With 3rd party equipment we don't have any support scope.
Sadly it might be best to look at a bell that works with VOIP.
Gareth_L