It may be that you live in an apartment, with montly service fees. Yearly the actual costs will be calculated and the balance will be mad. The advance paymennt can be adjusted and you could get a refund or need to pay extra.
We strive to within six months after closure of the season to establish accounts for servicecosts.
For this we sometimes, depend on third party data. It may be that this data is later than it should be delivered to us, which sometimes accounts can be established only in September.