Charged double for products I already paid for and own

I bought products from overseas and delivery company requested that I give them original invoice for items purchased. Customs wants me to pay the same amount again, for the items that I already bought, plus an extra 2.7% before they will give me my property. Money that I can't afford to pay, for items that I already paid for. And all I get from paying this ridiculous amount is that they hand the items to me. I already paid for the items, plus shipping and handling, why should I have to pay again?