SALES AS PER VAT RETURN DIFFERS FROM PL

You have to revise your sales tax returns. There is no other option. Why you say that you can not revise your returns.

The return cannot be revised as the mistake is found while preparing the VAT AUDIT of the concern and the last date of revised filing has elasped

If Vat Audit has been occured at your company then they (Vat Deptt) will raise penalty (extra vat payable) and there is no option to revise your vat return now and there will not be any problem with vat department in future as you will pay penalty on the same (on which mismatch with your books and vat returns)