A couple of things about this:
- You have to make sure you turn off the gas by turning the metallic handle thingy (not sure what its called) to the off position when you're not using your stove/oven.
- If after turning off the gas you still have the smell of gas then the proper thing is to call Metrogas to check all the connections for your apartment. However, a complaint to Metrogas usually ends up with gas disconnected for the whole building until they can make sure all is well. Maybe that's why your landlord doesn't want to deal with it.
- Either way, make sure you get a licensed gasista and not someone who "knows" how to fix stuff.
PS: Point # 2 above happened with my parents in law who called Metrogas for gas leakage problems and then the whole building didn't have gas for the whole month of July. So its only based on that that I told you about that. Not sure if its a general policy or not.