How much electricity do voltage stabilizers consume?
Here is a typical servo voltage stabilizer specification sheet: 



Efficiency will be given at full rated load, so if you have a 1kVA stabilizer it will waste about 40W. At less than full load, the losses and the efficiency will be less because there are two components to the losses- fixed and variable. The fixed loss for a good 1kVA variac (eg. Staco) might be 5-10W, and 98% at full load. So if we assume 10-20W fixed vampire loss for this Chinese one (no load), your no-load consumption would be around 7-15kWh/month. 

Since electricity costs around 10 cents US per kWh in many places where voltage stabilizers would be useful, that's about $1/month. 

If the stabilizer is boosting voltage that was otherwise low, or vice versa, to loads that are constant resistance (more or less) then the consumption will change because of that, but not by 3:1. So, your consumption should not be increased by much more than (say) 20% + 15kWh/month. 

Back in the old days, when people went around reading old-fashioned non-smart mechanical energy meters, there was sometimes a correction because the power company would estimate monthly power consumption based on previous usage patterns, and if the real situation was different there might be a relatively large correction when the estimates were reconciled with reality. Perhaps that is what you are seeing.