CCD — Staff complaint

I got a vouchercode from mydala.com that ill get a Free cappuccino on purchase of min 100 from ccd. Valid till 02oct. I went to this No. 58 Hm towers Brigade Road, Bangalore. So I bought Honey and Oat cookies of 150 and he took the Voucher code, he said its already used. So I called mydala staff and spoke to Bilal Ahmed and Told the ccd staff that im getting a new voucher code in the meanwhile ccd staff already made the bill for cookies and then Bilal called me to give me new voucher code and Ccd staff spoke to him as well and took a new code. But after disconnecting the call Staff asked me to buy new product again. But i told him that i already bought this cookie tin of 150. He said I have already made the bill now i will not use this code.
So why did he not tell me Before??? And this staff was so rude that he did not even say Sorry or accepted his mistake rather he asked me again to buy a new product. Why should I ? He said go to some other ccd and buy something else. Is this the way of talking to your Customers? And that too while answering he was not even looking at me . He was more interested in his Keyboard. I paid 40rs from Vodafone. All waste now. No use of that Voucher. That ccd staff was not even ashamed that its his mistake and How dare he say that to me to go to other Ccd and buy something else?on top of that he said he is the senior most staff. So is that the knowledge and behaviour of senior most Ccd staff .