Heating via ventilation with heat pump

Worse than in the forcibly ventilated concrete puffed rice cave it can't be

Well... I hear the words, but I lack the belief. Goethe, Faust..

Hello, me again.
I finally got an electricity bill for 2014/15. Photographed it and sent it via WhatsApp, and somehow at least the first page is missing, so it’s quite unclear.
To be honest, I’m pretty inexperienced when it comes to what heating costs for a single-family house should be, but this seems incredibly, insanely high to me.
Here are the key data again: timber-frame prefab house, about 145 sqm living space + finished, heated basement with sauna. Two people lived in the house back then.
If I read it correctly, they used 18,314 kWh heating electricity for 12 months = €3,762 net + 4,991 kWh usage electricity = €1,457 net.
That adds up to well over €5,200 including taxes in the year 2014.
Looking back at the previous year, it can also be seen that their consumption increased by 50%.

wow. Golden customer card, wall calendar at Christmas and a free terrace grill from the electricity provider in summer. That’s the customer you love.

There is something wrong there. Or is he heating the house with the sauna in the basement? I would just openly ask what is going on with that. 18,000 kWh heating electricity. Assuming that there is at least an annual performance factor of 3, that results in over 50,000 kWh of heat. Unbelievable. If there is no plausible answer to that, I would strongly advise against buying. Something is not right and anyone who does not play with open cards does not deserve trust.

To be honest, I am also shocked right now. I know that he had registered his company at this address at times. If he and his wife did office work at home all day, that might possibly explain a high bill regarding the "normal" electricity. But the actually worse thing is the heating electricity. He used to always beat around the bush when it came to talking about the electricity bill and said he always had a high bill because he used the cooling function of the pump a lot. But that is unbelievable at that amount, isn’t it?