regarding discounts

Aggarwal Marble (16 Points)

10 July 2017  
i am selling cementand paints
these companies issue bill of high rates for example: cement companies issued a bill of ₹340 and the cement sold lower of this price like cement sold to customer at 330rs and company should refund me discount after that.
then how should i issue my bill to customer as company is charging more tax
can i issue bill for rs 330 or more