I had this issue with IDNet which I believe use Zen Wholesale.
Went from a working service, mirgrated to IDNet and nothing. If all the lights are on with the ONT there is little an engineer can do.
The issue can be that the account isn't setup correctly, if they cancel and recreate the account it will probably spring into life. In my case they went through the process of booking an engineer but someone decided to recreate the account and everything sprung into life.
If a dialup connection from a computer to the ONT doesn't work, but the ONT lights are all green and as they should be, you have no need for an engineers visit at your house, and the issue is administrative their end.
Edited by E300 (Sun 09-May-21 14:05:50)