Violation Of Privacy Act

My required minimum payment to Capital One is $165.00 a month. I try to pay them, at least, twice a month to knock down finance charges. In December 2008 I paid a total of $378.00. The first week of January 2009 I mailed in $160.00 knowing in two weeks I would be mailing off another $160.00 payment. However, Capital One has suspended my account, and placed me in a collection agency due to my practices. The thing is, Capital One didn't contact me to notify me, they contacted my sister. My sister, who is not on ANY of my accounts, was contacted by Capital One on her home phone 3 times in a one week period. She was given my personal account information, and was asked how they could contact me. When I logged onto the website I noticed that Capital One has my cell phone number, my work number, my email address, and my billing address. How did this company receive my sister's home phone number? Why did they violate my privacy, and give her my information, not once, but three times? I called the customer service number on the back of my card January 29th, and I was told that SOMEONE gave them my sister's number. I called again January 30th, and was told by the account manager on duty, "We do not have any out of state numbers of contact for you, so I don't know what you're talking about. No one from this company contacted anyone in your family". What can I do as a consumer? Is this a common business practice?