You now know you're under investigation for theft (or at least accused). It's time for you to decline to make any further statements about this to ANYONE and find the best local criminal defense attorney you can. The dollar amount is in the misdemeanor range, but the fraudulent use of a credit card can be a felony. I'm not saying you will face felony charges, but it is possible. Don't mess around with this - a conviction will haunt you for years.
Look for an attorney that focuses on criminal defense, not just somebody who dabbles with criminal cases. Find an attorney that routinely practices in the court where this case may be heard.
Despite the name of the website, answers given are for information only and do NOT constitute legal advice. Every situation is unique and the complete case (all the facts and information) must be discussed in detail before an opinion can be given. Do not rely on any answers given on this site without consulting face to face with an attorney licensed to practice in the jurisdiction where your case is. Any answer given does NOT form an attorney-client relationship.