So it seems the cash shop didn't get that update where you can't refresh a confirmed purchase page anymore to get more of the item, because I just managed to buy 2 additional copies of an item by returning to that page.

First time I clicked a floating item, and since those currently take you to a whole other page I went back to the confirmed purchase page afterwards. When checking my inventory to use the item I saw I had 2 copies sitting in my inventory instead of the 1 I intended to purchase. Second time I went back to the purchase confirmed page and afterwards saw a additional copy of the item sitting in my inventory. Both unintended purchases took the item's csc cost out of my account. So the site is probably counting each visit to a cash shop purchase confirmed page as a purchase.

This bug can probably be recreated by refreshing the page you get after buying a single item from the cash shop (with enough csc on hand) or by purchasing an item going to another page and then returning to the previous page.

Already creating a ticket

This happened to me in June, not in the cash shop itself but with a purchase from the Hustler. I triple purchased by pressing the back button. I did create a ticket at the time and it was resolved that way but hopefully the code can be looked at if it wasn't already.