Boy I sure wish they would call me. We would be in court so fast it would make their head spin. By not answering you are effectively giving up all your rights, such as the right to a dunning letter telling you that you could dispute the debt, and also making it harder to prove that they are calling you.
Never heard of this caller before. There are so many scams out there that I do not answer numbers I do not know. I understand from other posters that this is some lowly debt collector. Thankfully, we have no debt other than our mortgage, so likely the caller is trying to reach someone else or scam us.