What to do if someone is using your home address on their bills?

A week ago we got a letter from a debt collecting service addressed to a woman we don't know but our address was on the envelope, thinking it was just a typo we sent the letter back and wrote on the envelope that no one with that name lived at that address. Now today we got a letter from the University's physicians which we ume is a bill, it has the same woman's name on it and our address again, is there anything else we should do besides send the letter back saying that that person doesn't live here? We built this house 20+ years ago so there is no way it is from someone who lived here before us.