Rate diffrance invoice

Dear All,

I have issued on 21st March 2013 invoice to our Customer For Rs. 1,00,000/- ( including Excise + Vat)

But now  we have notice that we have raised short amount invoice, Actual Amount is  1,30,000/- 

We have paid for the period Excise & Service Tax ( F Y 2012-2013 ) on the basis of invoice value Rs. 1,00,000/-

We said to party we will provide Debit note. but party is not accepting ( its our one of the major party so we cant force them to accept debit note / we explain them lot but they are not accepting debit note ).

Please give some solution

Thanks & regards,

Manish Parab