Telemarketing calls in the middle of the night?

I have an interesting situation - I live overseas in Germany and have a vonage phone with a west coast area code. We are getting ready to move back to the US and I called comcast to ask a question, I didn't give them the vonage number at all. Since then I've been getting calls about twice a day from their sales department but the problem is they see a west coast number not knowing that I'm 9 hours ahead of western time so the calls come at around 1 and 3 in the morning. I keep telling them that I live in Germany and have a vonage number and not to call again but it doesn't stop. I'm dying here - I just registered my number with the do not call registry but that can take up to 31 days. Is there anything I can say to them to make them take me seriously and take me off their damn call list? Can this be considered harassment or anything?