Ishop guys are having stupid system.
2 times payment gateway failed my 2 coupon of 500 rs wasted and it started saying coupon has been used already, after chatting and talking they failed to resolve the issue.
Then I just hit back the back button and used Internet banking instead of debit card and whoa it worked out, payment gateway to bank opened and payment done, so discount was received by me.
But seems that the security issues are there in their system