do i have to pay for a utility bill after i move out when it was in some one elses name?

my wife and i moved out due to me going to training for the coast guard at the end of august. some utilities where in one of the other tenants names due to this being a house. our lease says we pay 40% of the gas bill. we would always ask the person for the bill and she kept saying it wasent much and she just took care of it. when we moved out she told us she would email us the amount we owed her. our lease technicly ended july 15 and we where just on month to month after that. yesterday my wife told me that our old land lord sent out an email that the gas was shut off due to the bill being late. he paid for it and is now asking us to help pay for it, $303. i dont think i have to pay for it, but i dont know if that is what the law says. thanks for helping.