Suddenly costs me block storage fees and I cannot create an always free block storage anymore on my

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Hello,

I thought I can't use any paid resources on my free tier account, but "Cost Analysis" says I used paid block storage resources, suddenly since a few days ago.
I searched what happened for many hours, now I think this is a bug on oracle console.

After seeing the "Cost Analysis" report, I terminated my boot volume which is not labeled as 'Always Free' and a related instance.
I think I was unintentionally able to create a boot volumes over the limit (the number of always free block storage is 2, I had 3).
But oddly the fee of block storage are popped up a few days ago on 'Cost Analysis', though I created the third instance(boot volume) a week ago.