Collection Agency Scam?

Today I received a enveloped package, not a letter, via UPS and had to sign for it. In the package was a check for around $3,500 with all of my information on it from a company and address I had never heard of before. Of course naturally I googled the address and the company was located here:a href="http://www.csctulsa.org/" rel="nofollow"http://www.csctulsa.org//a along with the same address printed on the check but did not match the return address on the package. My mom then went to BBS and looked the company up to find out if the company was in fact legit, and found out it was a collection agency. Okay cool whatever the check is probably a fake or a scam but why would a collection agency be trying to scam me or send me fake money and how the heck did this company get all my contact information?