Portfolio Recovery Associates, Inc Scam collection call is constantly harrassing me Internet, Internet

I've been getting 4-5 calls weekly, sometimes late afternoons.  They have different people that call for them and ask for social security number, phone, and other information to verify my account. The first few calls I wouldnt give out my social security number or any infor to verfify myself. I ask them to mail me the info since they already have enough info to call. Now when they call they say I have a $2,300 debt to Capital One and they are a collection agency. I run a credit report every 6 months and have credit protection. I also, never had any debt to Capitol One since I never had a credit card.Whenever I ask to speak with a manager, they contsantly talk over me and don't listen to what I say. They show up now as an inquiry on my reports, but no other debt. Can they cause my credit score to lower if I don't have a debt? And can they keep calling even after I sent them a certified cease and disist letter by mail? I think they are a scam agency that makes up debt and tries to get people to pay off what they never owed.