Turn off the heat on your thermostat and get your family and pets out of the house immediately. Then call Sabre and your local gas company to report the problem. Someone will come out to shut off the gas and find out what’s causing the issue.
If you know where your gas meter is, you can shut the gas off yourself. You’ll see two pipes connected to your gas meter, one that goes into the ground and one that goes into the side of your home. Use a pipe wrench to turn off the valve coming from the ground (should be in the horizontal position). Even if you’re able to turn the gas off yourself, you still need to contact your gas company and an HVAC professional right away.