As of September 1, 2021, landlords can file an application for the tenants failure to comply with the utility costs with the LTB within one year from the date the tenant is no longer in possession of the rental unit. The tenant must have moved out of the rental unit on or after September 1, 2021. However, in order to file this application with the LTB, you will have to find out their new residential address to be able to serve them. The prescribed form is available on the LTB  at http://tribunalsontario.ca/ltb/forms/.