Phone #081-839-2539. Do not use the online rsvtn system - it has never worked. The problem you are having getting through by phone may have to do with the time of day you are calling. Try calling closer to the time they open (8pm).
If you are a small party, you don't really need reservations. We just generally arrive a few minutes before 8pm. The Italians (even those with reservations) don't begin to show up until well after 9pm.