HDFC Bank — cashback offered sanchay plus...now not picking call

On 4th June 2019, I got a call from Mr. Mayank from mobile [protected]. He proposed me the policy & told me to give cheque only today to get 17000 Rs cash back. I took the policy(policy no given above). Cashback decided to give as 5000 Rs in 1st installment and then 12000 Rs in 2nd installment.
First installment is not as per the timeline given by him, so he transferred me 5000 Rs from his personal account and told me that I will take these 5000 Rs from HDFC accounts by myself. It was transferred on 18 July 2019.
For another 12000 Rs, 90 days timeline was given which completes on 18 October 2019 but till now I did not get anything. Continuously following him through whatsapp & call but all in vain. Everytime gives me new date.
Mrs Sweta from HDFC accounts team called me also to confirm the 5000 Rs transfer in my account. But due to some server issues, 5000 Rs not transferred & that's why Mr. Mayank transferred from his personal account & took that 5000 Rs from HDFC accounts. Her mobile no is [protected]
From 2nd year, he told me to give premium waiver certificate so that I have to pay Rs 17000 less from 2nd year to 10th year.