Citibank — cash back not received from citibank

Address:

Mumbai

I had purchased perfume at Mumbai international airport terminal where i was suppose to get 15% cashback on using citi bank debit card.The seller said the amount will be credited in 90 days.Its already more than 90 days.
I am trying to reach citi bank since many days
But there customer service is terrible

There is no option to reach the customer care

Kindly assist at the earliest