Awful service and false advertising

I purchased 3 pairs of kids shoes for my boys as part of the the online black Friday specials, as well as other items. I received the package on Thursday, 25th November and only 2 pairs of the kids shoes came. The packing slip incorrectly started that the missing item was included. I called customer service and spoke to Grant who logged a call with the warehouse. They called on Saturday and spoke to my husband saying that they cannot find the shoes in the warehouse and because I had bought it on the 3 for 2 special, it was regarded as being free and they would not replace the shoes. The woman said the reasoning for this is that in the T&C's, it stated "while stocks last". When I ordered the shoes, there was stock so I have no idea why my baby should suffer without shoes. This is absolutely awful service and false advertising. They should clearly that state that if their poor stock management fails, it means you won't get what you order, that's not their problem.