Messages left at work for someone else

Yes and No

They can call you at work, unless they know you are not allowed calls there. They can speak to another person there, trying to locate you; however, they cannot give out personal information regarding you to that third party.

Unfortunately, this a gray area that some questionable CA's love to exploit. Can you give us more details regarding this situation?

My suggestion would be, if you don't want them contacting you at work, is to send them a Debt Validation letter and specifically state they are not to contact you at your job. Send this letter certified mail/return receipt requested. Theoretically, you should be able to just verbally advise the CA not to call you at work and they should stop; however, it seems to never happen this way. This is why a written request is usually better.