Hi @Lee Joon-ki ,
Q&A is community driven forums and for that reason we are not able to delete anything in Azure for a good reason.
the best option might be to open a support case with Microsoft Azure support for clarification.
Azure Billing and Subscription support is offered by Microsoft by no cost and it's for free.
Source: Azure Support plans
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards
Andreas Baumgarten