If gas is not mentioned nor charged within the first 6 months of the lease, can it be charged without notice at anytime?

When I signed my lease and during the first several months of my lease I was only charged water and garbage by a certain company. Without warning charges for gas started to show up on my utility bills and didn't have any information about it until I mentioned it to my landlord and they said that the company forgot to charge everyone in the complex and started billing when they realized it.