Amazon India - Package not delivere

Placed Ellica chimney order - * quantity on **th and the product delivered on **th with * qty. Courier agent said another will be delivered in couple of days as they received only *. After couple of days raised complain through customer support and on **nd they said investigation (internal) is done and the actual qty is delivered. The Tracking status shows the package is delivered and delivery receipt was signed but no one signed as my friends mother only received it. Poor service from amazon and i believe courier incharge has stolen the product. contacting support further said the investigation is closed and there is no further resolution. I am going through mental agony because of amazon. Please help on raising the complaint.