Stock unavailable but product advertised

Good day, I have taken out a new laptop contract for a Lenovo Slim 14 on 09/03/2021 and was advised I would be contacted as soon as the contract was approved and the laptop ready for collection.

The contract was approved on the same day but I was subsquently told there is no stock and the closest alternative was in a higher price bracket.

Please advise on the stock issue on my requested contract as this was what was advertised.