Hello @Ymm
It may help to explain how "missed call" and "voicemail notification" texts are designed to work.
Anytime a voicemail is left for you, a text message "from" the caller is sent to advise of the deposited message, alongside the spool symbol being toggled. If no CLI is present on the incoming call, the notification will be (IIRC) generic.
If, for whatever reason, your phone is unreachable for an incoming call but the caller doesn't leave a message, a "missed call" notification is generated along the same lines as above with respect to CLI.
Apart from the obvious suggestion of calling your voicemail (222 or speed-dial 1) to retrieve any deposited messages, which of the above scenarios is applicable? If necessary, you could post the exact text of the message you've received and we can advise further.
