Listing items with incorrect value

Very disappointed with MyUS.com. I bought $419.98 worth of items on Amazon and had it delivered to my MyUS box. They listed the value of the items that I shipped as $924.99, which increased the cost of insurance on the package and I can only imagine what the import taxes will be on a packet of that value. I've sent them numerous emails and the invoice from Amazon so that they can rectify their mistake and pay back the overcharged shipping cost, but I have received no response. I tried calling them as well and I only hear a message that says "This number does not exist". I tried to stop the package from being shipped with this incorrect value, but it kept automatically adding it to the shipping queue and eventually they subtracted the cost of shipping and insurance from my account even though I tried everything in my power to notify them of their mistake.