I tried to purchase a different plan online, but when I get to the online checkout and click 'upgrade an existing service' the screen shows the plan I've ordered but there's nowhere to click to finalise the order. Below the details there's a box that says to click here if you want to update. When I do that, it takes me to a page with mobile plans which I don't want. I seem to be stuck in a loop!
I came here to look for help on the same issue. All my attempts to upgrade my existing Mobile Broadband service have ended up at the plans for mobile phones. A couple of rounds with Codi and on hold for an hour (in high risk category) with no answer. The advice that deliveries are delayed makes taking out a new contract and then cancelling the existing one an option I cannot afford. Like you, I am in limbo.