I reckon you are receiving a government discount due to low consumption.
I've got a couple of condos that I visit through the week, use the swimming pool and gym. I only use the AC for a short while I shower, have a coffee etc.
My monthly bills are very low but last month and a few months earlier this year I got big discounts.
I assume the are looking after the poor.
Sadly I'm still paying several thousand baht a month for my house, no discount.