Sector 156 Noida: Builder promises vs reality shocking

Honestly not sure what to do. I booked a 3BHK in Sector 156 with [Builder Name] last year. They promised OC by Diwali. Still waiting. My kids' school admission depends on moving soon! EMI already start ho gayi hai. Sales team keeps saying 'sir, ho jaega'. Anyone else facing possession delay with [Builder Name]? What can I even do? Should I complain to RERA? My wife's really stressed.