Instant Systems Java Developer interview questions

I got the call from HR directly and she told me to take a telephonic round first and then other rounds will be face to face technical rounds and then HR round will be taken.

I got a call for the position of java developer . 1st round was telephonic interview , basic java questions were asked after that i was called for 2nd round at their office that was core java and spring hibernate interview , questions were average, after that i was again called for the third round with one senior guy , he asked to write a program and two puzzles . They offered me the position and asked for documents to release offer letter , once i had sent them documents there is no update from them i tried to contact someone from hr and she said sh also dont have update from team , its almost 15 days and they said the requirement was immediate , but still no update from there side.