Hey @Pashy! Philippe here. Thanks for contributing your first post. 
There's no fee to change your plan. The only fee would be if you ended an existing agreement by cancelling your line. The reason you can't go back to your old data-only plan online is that they're only available when you get a tablet. That said, we can probably do that for you, as an exception.
To do that, you'll need to contact us here or request a PM from the community.
