Issues after flat purchasing with old expenses

To give a bit of a context, I have purchased a flat end of last year and I have some issues with the old owner expenses.

Mainly, the owner claims he needs the last year invoices for the expenses, in order to calculate their part, which sounds reasonable. But the building administrator (who has the invoices) is totally unreachable both by me and the previous owner. We already gave notice to him because of that, but still the issue is not resolved.

My questions if anyone has any idea:

  1. Is there any way we can force the building administrator to do his work and send out a copy of the invoices? Cos, he just blocks us with the old expenses. Not sure if we need to send an official letter or something?
  2. If the previous owner would refuse to pay the expenses from last year, even after receiving the invoices (I dont believe it would happen, but what if), what should I do?

Many thanks!