Refund for revised return karnataka vat

Hi,

We have been filing Karnataka VAT returns regularly. Recently we noticed a mistake that (in March) we have double Invoiced a client (raised two Invoices for the same items). Without us noticing, VAT return was filed as usual in APR2013. Recently while preparing for IT rtns we noticed the mistake.

Considering we are in July 2013, what is the best way to correct this. Will filing a revised rtn entitle us to a refund (will the online system give us the credit after these 4~5 months, or will the dept. give us a refund by means of PO/Chq/DD)

Has anyone gone through this situation before? Please let me know the best procedure.

Thanks for your advice in advance.

Jothi