OPPO A78 5G
It's not possible to check my voicemail
Solution 5 of 6: You're trying to check your voicemail from another phone than your own
The default voicemail number can only be used if you're calling from your own phone.
Call 07953222222 to check your voice messages from another phone. Please note that you need to set a PIN before you can check your voice messages from another phone.