1) If your ex-boyfriend used your credit card without authoritization, you can certainly sue him; you probably cannot recover against the company he sent the money to, unless they knew (which is doubtful) that it was an unauthorized use of your card--otherwise, the company did nothing wrong, if they had no reason to believe that he could not use that card, and without fault, there probably is no basis for liability.2) You can sue him easily enough--you file a summons and complaint against him in court. For $6,000, you may wish to hire an attorney to do this for you--you'll pay probably $1,000 - $2,000 to the lawyer, but increase your chance of winning and also not have to be as personally involved in suing  someone with whom you have a history. Alternately, you could sue him in small claims court and represent yourself--the procedures in small claims court are more informal, so it's easier to act as your own lawyer there. Contact the small claims court: you get instructions, sample forms, and also check the jurisdictional limit, or how much you could sue for. (If the limit is less than $6,000, you'd have to either reduce what you are suing for, or else sue in county court, which probably calls for getting an attorney.)