Difficulty Upgrading

I am having a lot of difficulty upgrading.

I am eligible for one, and select my phone and plan but it won't let me get past the "My Details stage.

I keep pressing continue but it takes me to this message at the top of the screen, every time:

"These details can't be edited at this stage as we need to use the information currently held on your account for eligibility purposes."

it also tells me to edit my Details, which I have and it's still not letting me proceed.

I just want my new phone:(