IndiaCakes.com — Extra charges post payment confirmation

I placed an order for a 1/2kg cake to be delivered to my native place. I also received the order and payment confirmation of the same. Later after an hour I receive an email and message to pay extra 800rs. because only 1kg cake be delivered . When called the bad support team the agent said he cannot do anything and refund will be done in the form of coupon only.
I want my refund of the full amount paid to my account because I definitely do not wish to do any kind of transaction with Indiacakes in future