*Sigh* BTSSB Ordering issues

So I ordered a sold out item from there store before new years, and just when I thought they weren't going to reply (about 2 weeks later) they emailed me and accepted my order, but when I tried to add another (new, since they took so long to reply) item to the order they didn't reply, and now they've cancelled my order (12 days after I last emailed them) because I didn't pay. However, the reason I didn't pay yet is because I was waiting to hear from them, since I figured it would be a pain to send money that was less that the total order price if they added the other item. I ordered exactly the same way about a year ago, including adding items with no problems and their replies took 5-7 days. What should I do? And what is up with their incredibly slow replies at the moment?