I agree that it is hard to understand their billing system, I am still confused but I
think I get most of it.
This explanation may help you.
They take an initial reading and based on the information they have, they estimate the bill for the next year, based on your last years usage.
They divide this by 12 and bill you the same amount every month. This may explain why your bill is higher at the moment - its summer, your actual usage is lower than the average, but in winter your bills should be lower than before.
They only read the meter twice a year.
I am billed 77 a month so after 6 months, I have €462 credit. They do a meter reading, and calculate that I used €450 worth of electricity. I now have €12 credit, and the cycle starts again.
This is why the bill has strange amounts of credit on it at times.
In my case, they only recalculated the bill after a year and I got a new average bill for the next year.
If you find it too confusing, you might want to move back, but my bills are lower for the year, and I am not bothered that each bill does not reflect my actual usage that month, so I am OK with it.