Leakage from penthouse to below flat

Hi Sir, My penthouse resident is above my flat who is a tenant. I have leakages from his penthouse and has been complained several times but he denies allowing any plumber to enter his house to check the root problem even if I agree to pay to plumber for inspection. Following leakages 1) Bedroom Balcony (Leakage from penthouse kitchen) 2) Kitchen Balcony (Leakage from penthouse bathroom) 3) Bedroom Cupboard (Leakage from penthouse kitchen and basic washroom is the thing that is estimated) still proceeds and no fixes whatsoever have been finished The water spillage from penthouse walls gradually trickling out constantly making building dividers more fragile, Sticking smell and hurtful microorganisms development making an unhygienic environment. As I am directly under the level I am the promptly influenced inhabitant. As assessed from the most recent plumber and 3 different plumbers the spillage has obviously been referenced it must be fixed inside the penthouse kitchen and bathrooms. A Letter already available from latest plumber stating the same. Continuous requests were made to the inhabitant as we were not having direct owner who stays in US. None of the plumbers are being permitted inside the house for investigation into the penthouse nor any one have been suggested from the resident side to fix the issue. Owners Association is also not able to do anything as he is not cooperating and does not give the owners email or phone number. The owner has one more flat where his parents live and quite of old age and I did inform them and shown the pictures and videos. Please advice me on what I should do, I am really confused on how to deal this situation