Aiuto con bolletta elettrica esorbitante, dettagli nei commenti

So me and my wife recently moved out of an apartment into a new one. I just got the Schlussabrechnung for the old apartment and the bill is extremely high. It states (see pictures) that we used 4677 kWh over the course of a half year, that’s absolutely insane, right? They even provide a graph, where one can see that’s over twice the amount for a normal 4 person household. There are just two of us in a 75 sq.m. apartment, and I’m quite careful about electricity usage, with smart sockets and the like. We do have a couple “luxuries”, with an AC unit that we ran a few hours a day (never overnight) in the summer when temps reached above 30 C, and an electric dryer. Both are in the A class of efficiency (the dryer even A++). Nevertheless the costs from last two years were nowhere near this, we were actually below the average 1-person household despite the dryer and AC unit, so I’m convinced it can’t be due to these.

I’m thinking something went wrong with the meter reporting. I confirmed the usage just before moving out because I got a letter asking me to report it, so I went and read the meter and sent it back to them. The number matches what is in the invoice (50,611.00 kWh), and the starting number (45,934.00 kWh) matches what was on my Endabrechnung of my previous provider, but I didn’t take notice this high difference when I reported the 50611 figure a few weeks ago. The note “MB” seems to mean it came from “Messstellenbetreiber” which I looked it up and it seems to be the “Netzservice Karlsruhe”, who are indeed the ones that sent me that letter a few weeks ago asking me to report my Zählerstand, which I did think was weird because why would they be asking me and not my actual Anbieter (Lichtblick), but I chalked it up to it being a city service.

My question to those more experienced, since I don’t understand fully how the energy provider service works here:

1. Who do I call? Netzservice, lichtblick?
2. What exactly do I ask? Like how do I go about proving that’s the wrong number? There is just no possible way I used that much, like even if I really tried to… right? I mean how is that possible? That’s the number I read off sure, but something must be wrong. Our energy use last year is shown in the graph in the pictures too, you can see it’s about 1500 kWh, that’s for the whole year, we also had AC and dryer then, and that’s still below the 1-person average. Something is wrong, right? But how do I prove it?