I’m not a new customer and have been with PlusNet mobile at least 5 years but don’t think I’ve ever had working voicemail. I am assuming (but may be wrong?) that from 2019 at least, voicemail is included in all contracts. Callers are never asked to leave a message, and there is no setup option in my iPhone SE phone app. There is an engaged or dead line tone when I call voicemail or dial 555.
I have tried entering codes from other threads (**004*07870020555*11*30# and **004*+447870020555*11*30#). Both codes give the message “setting registration succeeded voice call forwarding all conditional calls”, but nothing changes, either before or after reboot.