Though you might need to contact Google if you are experiencing problems with the Store itself, there are a few things you can try first, to see if they get you back on track
The first thing to try is to restart your device. This usually reconnects and refreshes your links to the Store.
Also, make sure you have the latest update of the Google Play Store app installed.
Finally, clear the Google Play Store cache by using these steps:
- Open the Settings menu on your device.
- Go to Apps or Application Manager. (This option might differ depending on your device.)
- Scroll to All apps and then scroll down to the Google Play Store app.
- Open the app details and tap the Force stop button.
- Tap the Clear cache button.
- Repeat the steps above, but replace Google Play Store in step 3 with Google Play services.
You can find more support here in the Google Play Store Help page about purchase problems.
If you have any further issues which are not resolved by checking the above links, please get in touch.