No delivery of courier since almost a week

Location/place: New Delhi

Name of company/service: First Flight Couriers

I had to recieve an important letter from Citibank chennai and I havent recieved it as yet and when I ask cust service abt it they said I will recieve it by 6th aug but now no one answers on that no. Moreover when I contact the delivery branch Tilak Ngr new delhi they said that they have not recieved the consignment even by 8th aug in the evening. Citibank should not spoil their name by countinuing to have a tie up with First Flight.