Yes, you're right. Unfortunately that still only deleted all the other notifications but left the voicemail

I'll try your other suggestion later when I'm at home and can ssh into my Jolla, I find the terminal on the phone too fiddly.

This is the thing, with my service provider you can dial a number to disable voicemail and I did that when I first joined their service. I have never had a voicemail before and I shouldn't really be getting one now. I put the voicemail number in the settings and tried pressing the notification to dial the number in the hope that would get rid of it but of course it took me to an automated message telling me how to set up voicemail (which I didn't want to do) so I ended the call but the notification is still there.