A construction company having its HO in WB and registered under WB VAT Act. The company also registered with Assam VAT Act. In the year 2005-06 the company got a contract from NF Railway, Assam to build a bridge in Assam. For this purpose the company purchased iron & steels from outside of Bengal by using WB way bill in the year 2005-06 & 06-07, and also fabricated the bridge in WB. After fabricated the bridge was sent to Assam by using Assam way bill. Assam VAT was deducted by NF Rly, Assam and issue a certificate to us. In 2008-09 the company issue C form to supplier against the purchases made in 05-06 & 06-07. At the time of Assessment for the year 2008-09 the WB CTO demand VAT against the value of C form which was issue to supplier. Pls. advice how to VAT liability reduce.