To deactivate your voicemail, you just need to call 1987 (with your handset) and select option 4 “to deactivate or reactivate your voicemail.” By doing this, your voicemail will be directly deactivated.
To reactivate your voicemail, you just need to call 1987 (with your handset) and select option 4 “to deactivate or reactivate your voicemail.”