Selling something that is not there

On the 14th October 2026 I bought my twins watches for their birthday i was hoping they will be delivered between 5/7 working days, I paid for the delivery aswel, today 19th October I tracked the parcel only to find out they don't have them in stock. I feel it should have flagged that those watches are not there, they are waiting for a supplier, I should have not paid. Why did they let me pay for something that is not there, and to be told it will be available in 3weeks starting from now, I am beyond angry.