She removed her acoustic insulation. Who is responsible?

[SvN]

Dear all,

I would need a bit of advice

A claim was put to the insurance company to pay for the repair of the damage caused to my neighbour's flat due to a leak from my flat last Spring. The repair works have been done and paid for by the building's insurance.

But since the repair works in March 2009, the acoustic insulation of the ceiling has been much worse than it was before. She has rebuilt her ceiling but to save money, did not restore the ceiling insulation. This means that at normal levels, I can hear her and her TV as if she was in my flat. It is unbearable for me and for her, on a daily basis.

The builder told me that the money she saved by not putting back the insulation, she put in a wooden flooring and repainting the walls. It would make sense as she told me her flat is for sale now!

How can I have a guarantee from her that this problem will be sorted out before she sells it on? Who is responsible? Her, who asked the builder not to do the insulation to divert the money? The builder, who did not restore the ceiling to its original spec? The insurance, who paid for everything without checking that actually work had not been done properly?

I am in freehold and she is in leasehold.

The management does not want to be involved and says that:
" In accordance with the leases, the landlord has responsibility for the timbers, joists and beams of the floors and ceilings but does not have responsibility for the maintenance of the floors or ceilings themselves, which are the leaseholders responsibility, nor for the installation maintenance or otherwise of any insulation between the flats. We therefore suggest that you take this matter up directly with your neighbour and, obviously if necessary, through your own legal support." Is it true? Why did the insurance pay for the ceiling to be redone then?

If the flat is sold, will the new owners be responsible?

Thanks a lot.