Cst against "belated" c form

Dear Friends,

Thanks in Advance.

My Query is At the time of CST Sales, it is billed CST without C Form i.e., @ 5% / 13.5%  as the case may be.

We will remit to the govt the Tax Collected 5% / 13.5% as the case may be.

After Some time, the buyer gives the C Form to us.. AND get the differential CST (5%-2%) / (13.5%-2%) as a credit note.

Is it possible for us to Claim the Differential CST Paid from the Government?

If yes, what is the procedures to be followed ?

IF No, What we CAN do when we could not get the C Forms from the buyer for invoice raised against C Form..