Went through this for nearly a year. The escalation ladder that actually works: first, keep a written log with dates, times and descriptions of the noise, this evidence matters later. Second, since polite knocking failed, approach your Town Council and the HDB, they can send an advisory and mediate. Third, and often the most effective, apply to the Community Mediation Centre, it's low-cost, voluntary and many disputes genuinely resolve here because a neutral party is present. If mediation fails or they refuse, the Community Disputes Resolution Tribunal is the legal route, where you can seek orders and even damages, but treat that as a last resort because it strains the relationship permanently. Throughout, stay calm and documented, never retaliate with your own noise, that just lands you in trouble too. Sleep deprivation is serious, so start the log today.