Try to use this link: https://play.google.com/store/apps/deta ... roid&hl=en
Preferably use it with computer, not phone. When purchasing, use account you use on your phone as main account (in case you have more than one gmail account you use).
If you still have problems, then you should try get help with Google, as this is problem on their site. Game just uses Google infrastructure and calls it, within game itself (when you try to purchase from phone), as well as when you access Google Play Store.
So, we can't help you if you still have problems, as they are solely under Google's control.