Obviously if the Openreach tech ( or contractor working on their behalf ) encounter a problem they cannot resolve themselves, they pass the issue to whatever ‘back office’ department that does have the necessary systems access/knowledge/ etc. to resolve.
If the PON light is flashing on the ONT the optical path to the headend is established, but the ONT has not been authenticated (or cannot be authenticated) the installers job is completed, they can personally do no more with this situation, apart from advising the appropriate department.
The ISP statement that the installer won’t leave until all is tested is clearly subject to circumstances and predicated on a successful installation, if there is a problem like this , what possible benefit is derived by the installer staying put ?, whatever the issue is , it doesn’t need the installer to be at your property to resolve it.
You have simply been unfortunate that your installation failed , something that once your service is up and running you will be compensated for , if your previous copper pair based broadband has been ceased , as a consequence of combining the dates of the install date of the new service with the date of the cessation of the old service, that is also unfortunate but if avoiding even the possibility of having no service at all , (and of no use to you now , ) you may have been better advised to maintain the copper service until the FTTP was confirmed as working , and only then contacting your old provider to cease their copper based service, but presumably you wouldn’t have been happy about paying for 2 services but using only 1.
It’s a tiny percentage of installations ‘fail’ , it’s obviously of no comfort to you that yours was one of them , but to claim ‘mis- selling’ and threaten ‘legal action’ is somewhat hysterical , given its a domestic broadband service the installation of which may be delayed for a while , it no doubt sucks , but have a little sense of perspective
