I could say something glib "Like I am sure that is wrong" because of the compelling evidence you have presented.
However you have given any data.
Have you measured the items that you have connected for their consumption? (for this an inline power meter would be a good investment)
Have you checked the operation of the major energy consuming items to confirm they are operation correctly?
These items would include Fridges, Freezers, Air Conditioners, Electric Heaters, Hot Water Services, Incandescent Lights, Pumps, etc. For example if fridge/freezer door seals are leaking then it will operate normally but consume more power.
Just because the number of people have remained the same, it doesn't mean their consumption has done the same, especially if they are not paying the bills.