What can I do about a false fraud on accusation on myself?

My ex paid $1200 over the phone to a car shop to have my car fixed. That was 3 weeks ago when she was visiting but we both live in different houses in the state. I then get a call from the car shop yesterday saying the card was reported fraud by her and that I had to pay it! I texted her and she said I stole her card and had another girl call! I have her flight itinerary. Since she made a purchase in another state, wouldn't that prove she had her card on her? I also have text that don't really say she did it but they kind of do and it shows we talked about it.