Online upgrade can be selected, but is not possible

Vodacom has online deals and it includes the upgrade option, but when I try to upgrade I get the error: "You can't upgrade now. Find out why". When I click to find out why it says "You can upgrade, but not online." The same happened when I tried to upgrade my wife's line last month. When I upgrade on the phone they don't have the deals available and they only have the much more expensive upgrade options available. Why include an "Upgrade" option on your website when you cannot upgrade online? Either allow users to upgrade online or remove the option from your website.