They don't have any technical issues. They know that eBay would penalise them for making an out of stock cancellation. They also know that, ironically, eBay won't penalise them if they don't delivery anything and you have to use eBay's money back guarantee to get a refund. So that's what it suits them for you to do - never mind that it means you have to wait 30 days before even applying to get your money back.

This is pretty poor seller behaviour. They could have taken the penalty from eBay on the chin, and refunded you straight away. Or been honest with you about their problem, and asked you to help them by requesting a cancellation yourself - and maybe offered you a discount if you still wish to buy the correct iem when back in stock.

The options available to you have already been explained. I trust you will consider leaving feedback that alerts other buyers to this seller's conduct.