Is there a way to make iPhone forget an app?

I recently downloaded an app (Rival Knights) which I already had on my iPad, but not on my phone. It gave me the option to write over my saved data and I declined. However now, I've changed my mind and want to start again.

I've tried deleting and re-installing the app, completely resetting my iPhone, deleting the app from my game centre, and making a new apple ID, however none of these have worked.

Is there any other way I can make my phone forget the app so I have a chance of starting again?