HDFC Bank — regarding cancellation of policy (missale of policy)

Policy sold to me was missale so i want to cancel policy.
As i am writing mail to them but there is no proper revert from them.
I am following with them from month of march but till date there is no proper revert.
I had purchase policy in month of march only but due to some reason i was not able to cancelled in free look in period.
I requested them for full premium paid for three month.