The easiest way to deal with them is to tell them to automatically bill a credit card.
Metrogas is the one servicio you don't want cut off for non-payment. If they terminate your service, they won't restart it without checking your apartment for code compliance - which no apartment passes - and your building for gas leaks - which almost all buildings older than a few years suffer. If they find leaks, however minor, Metrogas will then turn off all service to the building until the consorcio raises the money to replace the gas distribution pipes throughout the building.
As for code compliance in your apartment, any room with a gas appliance needs permanently open vents at the ceiling and the floor within x meters of the appliance. Also no electrical devices that might ignite a gas leak are permitted in the general area of the gas appliance. So, for example, electric range hoods are illegal according to Metrogas, as are any lamps above a gas range. . . .