When Barclays attempt to call me on their secure monitored line it goes straight to my voicemail

[britvik]

When Barclays attempt to call my mobile on their secure line, they say it goes straight to my voicemail but my phone doesn't ring and I don't get a missed call notification. When they call me on a not so secure mobile phone then I receive the call. Is there a setting I can adjust or is it something tech support can sort out?

[MI5]

@britvik 

Have you enabled the blocking of unknown callers in the phone app?

This is a customer to customer community, not O2, so we cannot access your account, sorry.
You need to contact O2.
Message them on Social Media. Facebook (https://o2uk.co/O2CFB) , Twitter (https://o2uk.co/O2CTW) or Instagram (https://o2uk.co/O2CIG) or give them a call on 202 or 0344 809 0202 (contract) 4445 or 0344 8090222 (PAYG)