To cancel your Cloud Storage account, take the following steps:
Delete all your buckets and objects.
Disable the Cloud Storage services for your project.
For the desired project, open the list of enabled APIs in the Google Cloud Console. In the list of APIs, click Disable for Google Cloud Storage and Google Cloud Storage JSON API.
Disable billing (optional).
You do not incur any new Cloud Storage charges after you perform the above steps, but you can disable billing to stop receiving statements. You will receive one last bill for any remaining changes incurred between the beginning of the billing cycle and when you disabled billing.