Imperia Structures Limited — Assured return stopped, unit no not allotted & started sending maintenance bill

Sending maintenance bills without any allocation/possession o[censored]nit
Address: A-25, Mohan Cooperative Industrial Estate, Mathura Road, Near Sarita Vihar Metro Station

I have purchase one 500sqft space/unit at Imperia Mindspace (erstwhile Byron). It has stopped the assured returns long back. Now started sending Maintenance bill and asking to pay me. I have not received any allocation letter for the space/unit, building completion certificate... I tried calling them so many times and sending emails to them. Never picks up phone or replies on email.