Phantom call charges get regular mentions on here.
Does your landline connection come from the back of the VM hub or a conventional telephone wall socket?
It is helpful that you can see the number involved. Can you also see the times of day and duration of the phantom calls?
Phantom calls often follow a typical pattern of times of day and/or call duration.
We have also seen past cases on here where equipment in the home (such as burglar/care alarms and call blockers etc.) were running up call charges unexpectedly. Do you have any equipment like that connected to the phone line?