Why offer phones of which there is no stock?

Have just been through a lengthy upgrade process, telephonically (3 times in a week) to upgrade 3 numbers on my contract to iPhone SE (2020). Only to get phoned a week later saying there is no stock! SO WHY DOES THE SALES PERSON NOT KNOW THERE IS NO STOCK? AND WHY ON EARTH DO THEY OFFER YOU THE PHONE IF NO STOCK? No brainer of retail - know what you can deliver on. Pathetic MTN - really!