Not assigning stock to subscription

I have an ongoing subscription to a book series at my local CNA A few months ago they did not put aside the copy that was supposed to be for me and it was out of stock when I went to fetch it. I was apologised to and informed that it would never happen again. When I went to get my latest book I found that yet again, they had not bothered to put it aside for me and were yet again out of stock. First I was told that they had only revived one copy, then I was told that they had received more but had forgotten to put mine aside. I am very unhappy especially considering that I was assured that this would not be happening again yet the exact same thing occurred just a month later