Waltons @speed

If I could give zero stars I would!! So yesterday I was the first person to purchase using the new @speed service, I purchased 4 ink cartridges... When I received my order I only received 3 ink cartridges.. Then after calling and calling and no one answering the phone, I drove to the Waltons store and was told oh no sorry theres no stock of the yellow ink, and that they just launched this service so they still need to figure out what to do when an item is out of stock.. So they lady said she will speak to head office and then get back to me... Now I'm being told no I only paid for 3 ink cartridges, when I have it on sms, banking, email and the invoice from Waltons that clearly shows I paid for 4.. Still waiting to get this resolved...