State Bank Of India [SBI] — DD cancelled amount not yet credited to my account

Address: Udupi, Karnataka, 576104

I applied for Demand Draft (DD) through net banking and later I came to know that I have to collect the DD from base branch (Manipal) even though I mentioned IIT Powai branch IFSC code. Since it takes time to send DD from Manipal to Mumbai branch. I called them and asked to cancel my DD and credit the amount to my account. They asked me to mail request letter and counterfoil signed, which I did on the next day itself. After that whenever I call them they say we'll do it today and after one month they are not receiving my calls and not replying to my mails. It has been 3 and half months and I haven't received a penny back till now. Please help me so that I can get back my money.