I got the same call a few times. I don't think there is anyway you can stop them, but you can ignore them with the following:
I have an iPhone, but you can do this on any other phone.
I created a contact on my phone book and named it " DO NOT PICK UP" and I added this number to it. On most of the phones, you can have more than a few numbers, so I can add any other number that I do not want to answer to that contact.