I am sorry to learn of this situation. Unfortunately my advice here is going to be "Go hire a lawyer" (I know that customers do not come to this forum to be told that, but I am going to explain why, and I hope that you will understand that the string of events that has led you to this point has narrowed your options to the point that you really do need legal representation).
By filing a false "fraudulent transaction report" with your credit card companies you have actually committed fraud yourself.
The credit card carriers have no qualms whatsoever about referring these cases to local law enforcement which will then refer your matter to the District Attorney.
The amount in question can potentially raise the stakes of your matter to a felony (not just a misdemeanor charge).
Even if it was "only" a misdemeanor - a conviction for fraud of this type can have longstanding consequences as it is a "crime of moral turpitude" - meaning your honesty is now disputed making it harder for you to get many different types of jobs in the future, and can even bar you from volunteering in certain positions.
The fact that you haven't yet signed a declaration stating that the charges were fraudulent doesn't mean that you are no longer liable, but it can give your defense attorney a bit more room to work with (it isn't as damning as it could have been).
Hiring a criminal defense attorney now can help you negotiate a deal with the credit card company (a lawyer can negotiate a deal without having to admit guilt - it is very hard for you to do the same).