I need to know if I have been wrongfully terminated and what my options are.

I have been recently terminated from my job. They wrote dishonesty as the reason. I had used gift cards for purchases for work which usually they have a company card but there was not one available. A corporate supervisor had given them to me and did not ask I keep reciepts at all. I am an hourly employee and did shopping on my own time. Some items I got along wth my own purchases and did not get a seperate reciept. Another employee at a related company had been give gift cards to use and did not have to have any reciepts. However my new supervisor was constantly questioning me about my work. I accounted for all the purchases but they said I used poor judgement. I was never instructed to get reciepts and to my knowledge there are no policies regarding this issue. I also put a donation to a charity in the same way I had done for the charity the last time in 10/09. The charity does not accept cash so the charity said I could do it on line with credit card. I used my own both times. Now I am being accuse of being dishonest. I had not had any prior diciplinary actions and had been a dedicated and loyal employee for three and a half years. To my knowledge there is no policy on this either. Thank you.