Mobikwik - Cashback not received

I have paid my electricity bill of worth **** rs through mobikwik website on *th july ****.it has an offer of getting *** rs cashback on electricity bill payment above **** rs.while doing payment I had written the code killbill which is mandatory to get the cashback.but after the payment I have not received the cashback because accord to mobikwik personnel my code was not applied successfully but it's totally unbelievable because the code was written by me in full conscious state of mind and best of my knowledge.so,there is no any chance to commit mistake.If the code had not been applied successfully then it's their technical fault which can be checked easily but I think mobikwik does not have the will to give the cashback.kindly solve my problem.
my order numbers is mk***********