Upgrade says eligible but handset is still showing out of stock

Hi all, I got the text saying I’m upgrade eligible on my mobile, which is great, but every handset I click on says out of stock or delivery in 3-5 weeks. Bit of a pain really because I was hoping to sort it this weekend. Is the upgrade eligibility thing separate from stock, or am I doing something wrong? I’ve checked the app and the website and it’s the same on both.