Urgent help/advise with block property insurance claim

I live in a shared ownership flat on the 2nd floor/top floor of a block of flats. I have a 50% share. We had a water leak from the kitchen and bathroom to the flat below on two separate occasions. The washing machine was not installed properly and my son was using the shower. We found the source of the leak and rectified it within a couple of hours on each occasion. I have British Gas HomeCare agreement and I got the plumbers in to make sure the matter was resolved quickly. There was minor water damage in the kitchen ceiling and bathroom of the flat below. It was general maintenance repair (paint and decorate) which would be completed once it had dried out which took a week. All the leaseholders in our block pay service charge/building insurance via a management company.

I received an email on Thursday 12th April asking me to pay insurance schedule excess of £500 - see part of the email below .........

'Rxxx (the owner of no.54) has just received a copy of the block insurance schedule which shows he is required to pay £500 excess, which he will be claiming from yourself. We are trying to put this through as one claim for the kitchen and bathroom damage due to the same leak, however, there is a possibility the insurer may insist on it being put through as 2 separate claims and if this should be the case, we just wanted to let you know that Rxxxx will have no option but to claim the £1,000 excess charge from yourself'.

I rang them the owner of the flat below and explained I will have difficulty paying this as I have no contents insurance or savings and suggested if I could make instalment payments instead. The owner of the flat below claims we both have the same insurance policy (via property management company). I rang the property management company and I was told the building insurance covers the exterior and structural aspects of the block property only. Any damage to the interior/boundaries of each flat is the responsibility of the leaseholder. Furthermore, I was informed it is a private matter between myself and owner of the flat below.

Urgently need advice on what to do next?

Am I liable to pay this?

Am I right to ask to see a copy of block insurance schedule showing the demand for £500 excess payment and works carried out on the flat below?

If I have to pay this how can I ensure flat owners below will not ask me for more money?

Is it possible to pay them back by instalments? Otherwise, I will have to borrow the money to pay them.

Is it necessary to seek paid legal advice?

Very worried, don't want this to escalate and don't have the money to pay them or fight them through courts (if I am legally within my rights to do so).