Extra payment recd from customer

 Are you sure that the xyz co will not demand this money. If yes then treat this amount as Income.

cant treat this as income as all income heads and taxes thereon are finalised. can i raise invoice or show cash paid or what of this type i can do?

If you raising an Invoice for this amount then you have to reduce the stock also. As per fact there are no stock movement 

So if your can't take this in to income of this FY then transfer this amount  in Advance from customer and show in B/S as liabilities. 

If your accounts are already finalized, then let the balance of XYZ co, remain as it is in the balance sheet. You may write it back next year. 

book it as ur income but also consider the losses u have incurred

In present case you have received some advances from XYZ in earlier years & presently selling your product in normal course of transaction. In that case, its advisable that, before giving any effect of Written Off balance balance reconciliation should be done between parties.