hello prakhar...dont panic..i have checked ur application number on net..and it shows that it has been received as u told me also..it might be a case of postal delay...acknowledment card means only that ur application has reached which is otherwise confirmed by online update system as well..ur roll number will reach definitely..one of the possible case is u might not be at home when postman came to dlvr....i am not there at iit due to some other commitments...but u can if u want cm to the JEE office in IIT..however i wid suggest u to ask ur local postoffice and call JEE office only..
a 2nd year IIT DELHI student, doing B.Tech in chemical engineering