High input and low input

One of my client is a wholesale dealers of cement. Because of heavy competition in market , they are forced to give cement with less than cost price.This is possible , they are getting rebate and discount from their Main distributor. Because of this reason every month is Input is high and output is less.So they are are under refund in every month and is under less GP rate.The main distributor is not issuing credit note under invoice wise(that is discount is not traceable invoice wise).So they have no chance to reverse claimed input also.How to handle this situation.  GP is also less as compared to VAT period .