HDFC Bank — Complaint regarding non-receipt of promised Amazon voucher

I opened an account with HDFC Bank based on a promotional offer that included a reward of an Amazon voucher upon successful completion of certain requirements. I diligently fulfilled all the criteria stated in the offer and expected to receive the voucher within a reasonable time frame.
However, it has now been over two months since I met the necessary conditions, and I am yet to receive the promised voucher. I have contacted the customer service department on multiple occasions to inquire about the delay, but I have received no satisfactory response or resolution.