O2 Voicemail issue

[LIZS]

Using iPhone on O2. Caller has insisted they have left voicemail messages but none, either new or stored, are available to listen to on dialling 901 and not registered on missed or incoming call log. Possibly from a withheld number. Wondering if something has changed in Settings during an update. Any ideas please?

Why don't you get someone else to call and leave
a voicemail and check if it works

If it doesn't it's likely to be a carrier program not the phone