1050€ Nachzahlung is relatively high for a 50sq.m house. With the Nachzahlung request your Vermieter should also provide the bills supporting them.
- Do you have meters for house heating and warm water exclusively measuring your consumption. If so and your provide the bills supporting them, there is nothing much you can do rather than pay it?
- Did you record all the meter readings when you rented the apartment?
- What’s your billing period? April to April or dec to dec ?
- How is your warm water consumption and how is it heated. electric or gas?
- How good is your apartment insulated?
Without considering all these facts it’s difficult to say about Nachzahlung. It could be that you have just used too much of heating and warm water or it could also be that your Vermieter is unreasonable in his billing.
Before going up to the lawyer just check calculations by yourself. If there are separate meters then it's calculated according to your individual consumption. If not then the heating it
calculated/averaged according the
sq.m and the warm water according
to number of persons living in the apartment.
You have all the rights to ask and check for the bills. Comparing with the bills of pervious years will give you an idea of the average consumption in the house.
-coolguy