Dual sim and one number not receiving vm

[Qwerty123451]

Hi hopefully someone can help. My dual sim phone received voicemail successfully from both numbers until a few months ago . Now I can only receive vm from one of my numbers but the caller thinks they have left a message but unfortunately I do not get it.  Ive spoken to both staff at local O2 shop and Apple support but no success.  Thanks in advance 🤞🏼

[Bambino]

@Qwerty123451 Are both sims with O2 or is one with a different network? Have you spoken to O2 customer service? If not, call 202 from your mobile or 0800 032 1402 from any phone or numbers in this link: Guide: Coronavirus Community Help and Support 
When it comes to the reason you are calling, stay silent for 15 seconds and you will be taken to the keypad options.
Press 2 for Everything Else
Press 5 for More Options
Press 7 for Anything Else which will put you though to someone.
Say 'Upgrade', 'Lost/Stolen', or 'Fraud' if the suggestion above doesn't get you through.
Best time to call is 8 am.

[RafaC]

Hey @Qwerty123451 did you manage to solve this issue already?