Thank you all for your valuable comments and advice.
Chipcity this is extremely useful to know where to go.

I have checked the Land Registry again and the leaseholder/freeholder address for the property upstairs is the same as it is on our lease documents - it is not their actual address. The name is the grandfather of woman i am dealing with whom I have never seen.
With regards to the service charge - there is none and £150 pa for ground rent that have never been claimed by the freeholder. I stopped worrying about not paying when I realised they do not maintain the property at all but should I ask them for it? From the below regulation I assume that I do not have to do it unless it is properly demanded.
The previous owner re-assured us through the solicitors that books are up to date and that there were no disputes but do not think these were seen by anyone and I suspect that he just did not inform us what was going on but these problems existed before.

Would on-line small claims Money Claim be suitable place to start recovering the excess money £500 the landlords was supposed to pay us back due to the leak in the kitchen before? They said they would cover it but never showed up since then.

It looks like the only way forward would be to use legal help. Just a bit concerned this may be costly exercise, but given we cannot just sell and move right now, it may be the only one

Thanks for your help. Really appreciate.