PayAsYouGo Billing active when APEX service + DB (ATP) is in STOPPED status

Dear Oracle experts.

I am using the APEX Development service on cloud using the PayAsYouGo billing method. Recently, I changed the status of the APEX instance to STOPPED (this also stops the underlying database) for about 8 hours. However, the next day I checked and found that the PayAsYouGo billing for the database was active for the hours when the service was in STOPPED status.

Could anyone explain to me what the cause of this is ?

I will be very grateful. Thanks in advance.