Since you have already informed both the owner and the tenant and there has been no improvement, the next logical and legally sound step is to proceed with a police complaint first, followed by a legal notice if the disturbance continues.
You do not need to go directly to court at this stage. Law expects you to first exhaust simpler and immediate remedies, and police intervention in nuisance cases is considered an appropriate second step. A written police complaint creates an official record and often acts as an effective deterrent without escalating the dispute unnecessarily.
You should submit a written complaint to the local police station describing the nature of disturbance, the frequency, the time period (especially late-night noise), and the fact that prior intimation to both the tenant and the owner has failed. Clearly state that the noise is continuous, avoidable, and affecting your health and peaceful living. Police usually issue a warning, call the tenant for counselling, or visit the premises, which in many cases resolves the issue.
If police intervention does not help or the disturbance resumes, then you should proceed with a legal notice addressed to both the owner and the tenant. The notice should record the history of disturbance, prior complaints, police intimation (if any), and clearly state that continued nuisance will compel you to seek court injunction. Sending a legal notice before filing a case strengthens your position and shows that you acted reasonably.
As far as proof is concerned, maintaining a disturbance log is very important. A handwritten or typed log noting date, time, duration, and nature of noise is valid supporting evidence. Audio or video recordings from inside your flat are also relevant. Using an Android decibel meter app is helpful as a corroborative tool, but by itself it is not conclusive scientific evidence. Courts treat such readings as supporting material, not as the sole proof. What matters more is the pattern, frequency, and impact of the disturbance.
If possible, recordings that capture both the noise and the time (such as screen recording while the decibel app is running) are better. Even normal audio recordings demonstrating loud and repetitive sounds late at night are sufficient at this stage. Independent corroboration from another neighbour, if available, further strengthens your case, but it is not mandatory.
If the issue still persists despite police warning and legal notice, you can file a civil suit for permanent and mandatory injunction seeking restraint on nuisance. Courts do entertain such matters even where the society is unregistered and managed by an ad hoc committee.
In summary, proceed first with a written police complaint, continue maintaining a disturbance log and recordings, and escalate to a legal notice only if required. This sequence is legally appropriate, proportionate, and strengthens your case if court intervention becomes necessary.