Call customer service at 1-888-294-6804 and they can block that number for you.
No they can't.
There are two options:
1) Change your number
2) Set up a restriction on your phone so anyone who is NOT listed in your contacts will NOT be able to call you.
Kinda like a VIP list for a club. If you're not on the list, you don't get in.
Best solution: put number into your contacts, and set ringer to None. That way, you will have a record of calls, but will not be bothered by the calls. If voice messages are left, you can delete without listening.