First things first: it's important to first secure your account to stop this happening again. I would recommend:
- Changing the password to your Google or Apple account. Make sure it's changed to something unique and secure, and that you don't share it with anyone else.
- Enabling additional security on your device that means that no purchases can be made without additional checks. Both Apple and Google provide these features - please follow the relevant links below for more information.
Only Apple themselves can refund purchases made on iOS - this is not something a developer like SEGA can do themselves. If you do have an unauthorised purchase on your account please contact Apple directly for more help. You can reach Apple's support team here:
Android / Google
If you have an unauthorised purchase on Google Play, Google may be able to assist you further. Please contact their support team here: