Citicard Billing Dispute Problems

I was charged on my bill for around $72 for a gas charge in Cancun, Mexico. The receipt which I kept showed the amount to be around 320 Pesos which equals around $32. Before sending the information I asked billing how I should handle the conversion from Pesos to dollars to compute the disputed amount. They told me to just send the info and they will handle the conversion. I faxed all the information, including the original receipt to the billing dept. Then a month later I got a letter stating they did not receive the fax. So I sent all the information again. Then weeks later I got a letter stating they need to know the original amount. So I called them again and explained the issue. The first person I spoke to said that I was charged 770 pesos, but they would not do the conversion for me. So I asked to speak to a supervisor. She told me she didn't know how many pesos I was charged and that I had to call the merchant (which of course I cannot, nor would that do any good I am sure). Basically she could not tell me what information they wanted. When I asked if I should do the conversion, she just kept saying that I need to call the merchant. It was incredible, what should have been a simple matter ended up taking hours of my time. Finally I spoke to a supervisor in customer service who seemed more will to help. I am awaiting word on whether this will be resolved. Watch out if you have a disputed charge in a foreign country from citicard mastercard.