Welcome to the community and thanks for posting. I deeply apologise for the error message when trying to upgrade online. I appreciate it's annoying for you because it's designed to make things easier.
It appears the person on the phone had this raised up to the IT department when you called as there was something blocking it from progressing. I'm sorry you were cut off too, I'm sure this wasn't intentional.
I tried ordering online earlier and got further than ever but fell at the final hurdle. Despite putting my debit card name in correctly (and all other card details), the process refused to accept it. I've tried different variations. No luck. It doesn't seem to be human error but I'm losing patience.