Clarification on excise & cst payments

Dear sir

We are manufacturing Electrical items. we supplied the material to  "X" party at Gujarath on 25/03/2012 and raised the Excise & Commercial invoice on the same day and paid excise & cst on due dates.

but transporter was delivered the goods on 05/05/2012 instead off 31/03/2012 and goods are accepted by the customer. 

Now customer is  not accepting  Excise & Commercial invoice partaining to the financial year 2011-12 and they insting us to raise the  new invoice during the financial year of 2012-13. in view of the above how to raise the new invoice without making excise & CST payments, since we have already paid taxes in the year 2011-12