Cellphone Deal gone wrong

I bought a phone online on the 14th February 2023 which was on Special from Arbour Crossing and there was on item left instore. In the morning as I was arranging for courier services with them, I received an email that the item was sold instore. How can an item that has been bought already sold to another client? Does that mean that items can be sold to two or more people at the same time. I am not happy at all with the service that Cash Converters has provided me with. They have told me I will be refunded. When i engaged the administrator he was very rude. How can such a big business make such an error???