Dear Customer (name blocked for privacy),
Because of the amount of "phishing" going on in the world today, and to make sure that this person is, indeed, from your credit card company, you should call your credit card company and ask them if your account is overlimit. If it is, then ask if they have been calling you? This can help you verify if this is a "real" call or if it may be phishing to get your information for possible ID theft. If it turns out they have been calling you, and contacting your employer, then you can tell them to stop. If they do not stop you may want to investigate filing charges against them for costing you your job with an attorney.
If it is a collection company, then they have rules they need to follow and you can report their calls, talking to your employer (which they can't do) to the Federal Trade Commission at http://www.ftc.gov/bcp/conline/pubs/credit/fdc.shtm
If it turns out you are NOT overlimit, then you may want to report this to the FL Attorney General's office AND get a copy of their Identity Theft Victim kit - http://myfloridalegal.com/identitytheft
PLEASE NOTE: Responses here are for information/education only, NOT legal advice and do not form attorney-client relationship! Only licensed attorneys you hire in your state can provide legal advice.