Retrieving O2 Voicemail on FP2

I cannot access O2 Voicemail messages that I get notified about. When I tap on “New Voicemail CARD1” - it dials someone called “Voicemail” who tells me that the number cannot be found. Seen a few suggested methods to enter 901 etc - but I am not presented with this as an option in my Phone App settings.

A post was merged into an existing topic: How do I retrieve voicemail messages?