Try sending another email to David. I had some problems with an order and emails went unanswered. I finally tried again and David responded immediately, stating that they were training a new guy for the web site and he was "very confused" by some of the emails. In other words, what he didn't understand, he didn't respond to. After finally getting thru to David, it sounds like my problem has been resolved? Haven't received the package yet, but have been assured it is on it's way. I went directly to the web site, waited until I saw David was online, then sent my email. He responded within the hour. I would give that a try. Good luck.
I also had problems receiving a reply from david yang and think the training a new guy was just an excuse. I sent 2 email on the 15th and 16th and have never received a reply. I don't think it is actually david yang that replies to all the emails. I believe it is an auto signature because I sent for a lost password and got one instantly saying it was from him.