According to the Fair Debt Collection Act, if you ask them not to call you at work and they continue to do so, you can file a claim against them as it is ILLEGAL for them to call you at work if you tell them not to. See www.ftc.gov and do a search on Fair Debt Collection.
Called and I did not recognize the number. They did not leave a message. I did go and check out the number on whitepages.com and it gave a name and address that I have listed below