unfair business practice

I gave a cheque no.194044 dated 8th aug 2008 for Rs 40000/- for a fixed deposit for 30 months .The company received this money on 16th august 08.by debit to my bank acct on this date.The company has sent me a fixed deposit receipt no.333H0043734 dt 5th sept 08 which says date of deposit 30aug 08.This means they are keeping my money without paying me any interest from 16th to 30th august which is plain cheating.