Sales tax notice

MY CLIENT (RETAILER) HAS RECEIVED A NOTICE FROM SALES TAX DEPARTMENT TO PAY 60000/- (VAT +PENALTY+INTEREST) FOR NON PAYMENT OF SAME BY DEALER FROM WHOM CLIENT HAS PURCHSED 4 YEARS BACK.........HE HAD ALREADY PAID THE VAT AMOUNT TO DEALER AT THE TIME OF PURCHASE AND TAKEN SET OFF THAT TIME .BUT THAT DEALER HAS CANCELLED HIS REGISTRATION AND RUN AWAY..DEPT IS SENDING NOTICE OF SET OFF CANCELLATION AS HAWALA TRANSACTION AND DEMANDING TO PAY THE ABOVE AMOUNT....CAN ANY ONE GUIDE ME OF WHAT TO DO IN THIS SITUATION.....IS IT LEGAL TO MAKE DEMAND FROM THE CLIENT FOR SUCH DEFAULT OF DEALER......