accused of identy theft via credit card. how do i correct this situation?

After our seperation, my exfiance accused me of stealing his credit card even after i had my own card with my name on it. All our transactions went thru the computer. e-bills, statements etc. I have not used this particular card since our seperation. How do I correct this situation. My insurance quotes have gone up, stores that I frequent look at me differently. I called the credit card that was in question and talked to the investigators who stated that no one has been put on the case yet. I explained how this was being done out of retaliation, that he just didn't want to pay the bill and why was I not informed of the accusations or a warrant had not been issued, yet I was having to suffer with my credit reports. I need to now what step to take next and do I pursue legal action against him for defamation of caracter, slander etc. Please help