Thanks for your post @pete39 and Welcome to the Community!
The only way we're able to activate/ deactivate your Voicemail is from our system. You can do this by dialing 500 from your SIM, 0800 0791133 from another line; or you can contact our Live-Chat Team via https://www.plus.net/mobile/.
You can also send me a private message on here.
We'll just need for you confirm, in your PM:
- Your full name and that you are the account holder.