Thanks for taking the time to reply.
Other than my wife spending a night or two each month the house has been unoccupied for 4+ years and yes we have received and paid monthly bills. Around 1,000bht, even though unoccupied 2 fridges and the odd light.
I work offshore so can't carry out the steps suggested. I'll get my wife to arrange a sparky, if such a thing exists.
There would be 10+ years of records showing that consumption has not exceeded 2000bht. Then logic would show that a jump to 16,000bht for one month clearly shows an issue.
And yes, I know logic rarely, if ever exists in Thailand.
KhunLa thanks for the tip on leeching. We are rural and shall investigate.