All purchasing is handled directly by your App Store and not by us, so their Support Team is better equipped to resolve this issue for you.
On iOS:
Please try these troubleshooting steps: https://support.apple.com/en-us/HT203005
If you still need help, please contact Apple Support: https://support.apple.com/contact
On Android
Please try these troubleshooting steps: https://support.google.com/googleplay/answer/1267137?hl=en&ref_topic=3365267
If you still need help, please contact Google Play Support.
On Amazon
Please contact Amazon Support: https://www.amazon.com/gp/help/customer/contact-us