Problem occurred while adding credit card but payment was successfully proceeded. Refund?

Summary:

Adding credit card failed but successfully paid 2 x 138.19 Singapore dollars. How can I request a refund?

Content (please ensure you mask any confidential information):

Hi.

I have been using an OCI Free Tier account for over 3 years. Recently, I wanted to use servers across different regions, so I attempted to upgrade to a paid account.

On May 12, I logged into the OCI console and followed the prompt to add a credit card and clicked "Upgrade."
However, a red message appeared in the upper right corner of the page saying there was a payment problem and the adding failed.
After that, the credit card I added disappeared from the payment methods list, and the system still asked me to add a payment method.