MP Consol India Pvt Ltd Chennai - Incorrect invoice

I had a shipment (my household goods) transferred from U.K. to Bangalore, India by sea freight in July ****. The shipping line directly appointed MP Consol India pVt Ltd in Chennai as agent at port of destination. MP consol India Pvt Ltd, Chennai has sent me an invoice which is exorbitantly high. I had already prepaid all freight charges from U.K. to Bangalore, India. They are charging me $***/- for personal effects other than the usual terminal charges, documentation fees, service fees, cargo handling charges etc.,. When I asked them what this fee for personal charges are, they said that an agent in Colombo which was the transit port has asked them to collect this amount of $***/-. I called up the Colombo agent who informed me that it is MP Consol who told them that it is to pay customs in Chennai, India. They have not done any custom clearance in Chennai as I am doing it myself in Bangalore. When I asked them as to whom they have paid this amount and the evidence for it, they have not replied back. They are demanding that I pay this extra amount else I won’t get my delivery order without which I cannot pick up my consignment. I am still paying the storage charges for the same.