Return Item Chargeback

I was hit with a Return Item Chargeback today from my bank in the amount of $298.87, they told me that it happend on the 10th of October 2008. They couldnt find any extra information as to how it happend, they said that it was a check that I cashed for $298.87 and said only I could have done it since I have a State ID. I asked to dispute it they told me they will do more research on it and they asked if I could call Monday. If this is not resolved and they say that I still owe them what should I do? The only checks I ever cash at my bank is from my job I never recieved a $298.87 check from my job I have proof from my paycheck stubs.