Can you borrow someone else's phone and put your SIM in their phone? And put their SIM in your phone while you're at it? That should pinpoint the problem as to whether it's the SIM/plan or the phone.
No, the FAQ is unclear. You use minutes in your plan if you are calling from your mobile phone and you leave a voicemail on someone else's mailbox. If someone is calling your mobile phone, and you don't pick up and it goes to voicemail, your minutes ...