I was tracking the support ticket and I'm glad that you were able to resolve your issue. I will post the solution here so that others experiencing the same thing can reference this!
Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to "Accept " the answer. Accepted answers show up at the top, resulting in improved discoverability for others.
Issue: Cannot delete storage account.
Cause: Pending migration from classic to ARM.
Solution: Worked with the support engineer and followed the steps to migrate the storage account from classic to ARM and then were able to delete the storage account.
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