subsequent sale

I got a works contract of supply & errection with electricity deptt. I purchased the material and made sale in transit to the contractee who returned the goods to me which I errected . The contractee deducted 4% TDS on supply portion . I claimed refund from the VAT deptt .the officer refused to refund . The contractee issued "C" form to me and I have also got form E-1 . I produced the same to AO. My question is how can I prove the sale as transit /subsequent sale? and get back the refund.