Not that I know of I'm afraid. To be brutally honest, your best bet for topping up if you're on E.On Next is to just go down to any PayPoint or Payzone shop and top-up there whenever possible, even if you have smart meters. Not only does this bypass the broken website systems, you'll also get a paper receipt with the UTRN on it, so that you can force the top-up through manually directly on the meters if it fails to go through automatically. Any other method is likely to be unreliable. If you need to be able to top-up online or via a mobile app, you might want to switch supplier.