Upgrade says eligible but handset is showing out of stock

Hi all, hoping someone can explain this because I’m going round in circles. My account says I’m eligible for an upgrade on my mobile, but when I pick the phone it says out of stock. It’s been like that for 9 days now. I’m on the 24-month plan, nothing weird with the account as far as I know. I just want to keep my number and move onto a new handset, but the site keeps letting me get right to the end and then bounces me out. Is this normal or is it actually stuck?