Again I can only judge on what those in this thread has said but stepping out of the phase change business seems smart here.
If you can not deliver the products that you promised on time or at least within a decent time frame of order then you have no business to begin with. Number one rule of business in my industry is that you have to keep the customers happy no matter what, if you do that then you have won half the battle already and are more likely to have them return and talk positively about you.
Here you haven't managed that and I would think it wise to reduce the damage done here by stopping all future orders as you have already done and just bite the bullet and refund those that have yet to see their products.