It’s possible that you’ve turned on the Automatically  apply credits option, CF2020.

Please follow the steps below on how to verify if you’ve turned it on:

1. Click the Gear icon, and then select Account and Settings.
2. Go to the Advanced tab.
3. Click the pencil (edit) icon on the Automation row.
4. Deselect Automatically apply credits box.
5. Click Save, and then Done.

You can also take a look at this article about the Advanced tab: How do I set my advanced account settings?.

Please let me know if you have other concerns. Thank you!