Custom Tax

Dear All, I am stuck with DHL and Custom while importing certain electronics item for my study in radio electronic I have purchased the follwing item 1) DC Power supply 1 Piece 2) Radio antenna with wire 1 PC 3) Auto Tuner 1 PC 4)Frequency Meter 1 PC 5)Line isolator 1 PC 6) some connectors to join cable 6 PC 7) Patch cable 1 PC All this item were brought from different seller and forwarded to a forwarding agent in US One seller has devalued the item from some where $300 to $30 All Item has Invoice The forwarding agent has provided a itemised Invoice based on merchant invoice(also attached merchant invoice with shipment) and since one merchant as devalued one invoice hence total value of shipment is devalued DHL informed Custom has query about Value and wanted to payment receipt for this imported item. I do not have any payment receipt I have only Payment receipt of forwarding agent who has charged me for forwarding the item from USA to India. Since I donot have payment receipt DHL is asking me to give a letter addressed to assistant commisioner of custom stating that the mentioned item in itemised Invoice is on FOC (free of charge) .Hence requesting custom official to enhance the value and process the clearance. Please suggest what should I do. Thanks in advance