ViolationFine for not having a ticket on a Florence bus

Hello, just looking for input on this... We were taking the C2 bus in historic Florence and were advised we could buy a ticket aboard the bus from the driver. However when we got on the bus and tried to give the driver the 2 euro fare I believe he said he could not sell us the ticket and would not take our money. This Despite the fact there was a sign saying tickets were for sale. We were confused and there was a language barrier for sure but two young girls were were also on the bus told us the driver had just sold them tickets. Two stops later the transit authorities boarded the bus and approached us directly asking for payment of the 50 euro fine. Our attempt to communicate the situation got us nowhere and finally we were advised we could dispute the fine at their office at Santa Maria novella. So off we went however we could not get an English speaking employee and they gave us an email address. This is not the case of not validating a ticket or trying to ride for free. Any advice is appreciated. I don't want to pay the 50 euros based on what happened but I'm not sure how successful our argument and don't know the consequences of not paying or what happens if we dispute and lose. Any advise is appreciated.