Apparently “sold out” and “in stock” mean the same thing

Ordered a sweater that was on sale and paid at checkout with my debit card. When I went to “track order” the next day it went from “processed” to “cancelled”. I called them to ask what was going on, they said that there was an inventory error and there was nothing they could do and that they probably wouldn’t be restocking the item since it was on sale. Horrible customer service. When you put something in your cart that says IN STOCK and PAY FOR IT you expect to get that item and not “a refund within 5 working days”.