5% cash back on SBI credit card new year offer

Dear Sir/ Madam

I purchased hp n series laptop during new year offer on 6th January 2014 with an 5% cash back offer on sbi credit card.

However, i have yet to receive the cash back  in to my account yet. The hp stores person at chandigah , where i purchased my laptop, told me that I will get amount credited within 3 days but it is now almost a month.

So kindly let me know what needs to be done next?