Are charges supposed to be this high??

This is a plot of my Atmos Energy bills since I bought my house. I didn't know gas bills could be this high. This is my first home (yes, an older home, 1973 but well maintained). I lived in a ratty old duplex through college and before I bought this house, and my energy bills were always relatively steady, I think between $25-$45/month for all four years.
How can a bill vary and skyrocket this much? I called them last winter thinking there must be some leak or some mistake Obviously it's higher in the winter months - is this what it costs to heat a home? I keep the heater at 67 degrees. I was charged $270 last month (because their billing got off cycle and I didn't get a charge in January).
What can I do about this?

This is a plot of my Atmos Energy bills since I bought my house. I didn't know gas bills could be this high. This is my first home (yes, an older home, 1973 but well maintained). I lived in a ratty old duplex through college and before I bought this house, and my energy bills were always relatively steady, I think between $25-$45/month for all four years.
How can a bill vary and skyrocket this much? I called them last winter thinking there must be some leak or some mistake Obviously it's higher in the winter months - is this what it costs to heat a home? I keep the heater at 67 degrees. I was charged $270 last month (because their billing got off cycle and I didn't get a charge in January).
What can I do about this?