As with most downloadable software products, all Virtual Items purchased by you are non-refundable. You'll need to contact Google/Apple for refund requests. They will help you in detail. The equivalent number of diamonds to the amount you refunded will be deducted from your account. Since some players abuse this; 3 or more reimbursed accounts are automatically banned by the system.
What should I do if someone has made an unauthorized purchase on my account?
You are responsible for the security of your account and ensuring that no unauthorized purchases occur on your account. Masomo is not liable for any unauthorized purchases (including fraudulent purchases or purchases made by minors). If you wish to pursue a refund for such purchases, you should contact your bank or the payment provider such as the relevant app store.