Great Eastern Appliances — After billing push me to take other brand due to empty stock

Address:

Kolkata, West Bengal, 700006

I had go to kakurgachi great eastern appliances pvt ltd to purchese a godrej gsc 12dg3 1 ton split ac. After billing (Invoice no: kg/sa/1718/03193, invoice date:[protected] the sales manager inform me that the have no stock of that product, and try to pull me to choose another brand and claiming me to pay the extra amount.
While i disagree with them the finance executive mithu dutta tell me that it is not possible to cancel the order.
Please tell me what i have to do?

Regards,
S. Das