Always out of stock but taking payment

I had purchased a pair of crocs with it say 1 in stock, immediately after it said sold out, I was told that they pack orders based on whatever invoice is on the top not if i had purchased before someone else.

It took them more than 48hrs to even check my invoice, if I had never contacted them on email, it would have been forgotten, I dont understand how this mishap, happens all the time, ive had a few people have the same issue?

They can only say sorry and refund with no thought afterwards.