Photocopy everything, including proof of your payment. Write a letter asking them when they intend to ship the remainder of your order. Send it certified mail, return receipt requested, to either the office where you placed the order, or to the address listed on the paperwork that came with the merchandise which did arrive.
Let us know if that gets their attention. I know that we all love to take care of things with a simple phone call, but that's apparently NOT working right now. Time for different tactics.
