Good day Peter, would like to find out if its allowed if I bought something online promotion and it went through (last week monday)

Good day Peter, would like to find out if its allowed if I bought something online promotion and it went through (last week monday) .then after a day they called and said the r out of stock while I was supposed to collect? Then I told them I will wait till they receive stock, then today again they called said they want to cancel my order as the item is out of stock and discontinued?