Okay, Green, 

I had to go back and read the last paragraph of your query, you will like to know the sites that use the biggest amount of storage.

 

This is what I will suggest, 

Navigate to the SharePoint admin center (Modern Experience) and filter it with the largest sites and that should display the page in top-down of sites with the highest usage, after doing this you can visit the site itself to pick well-detailed storage metrics once you a site collection admin on the site.

As for the support request with Microsoft, I will advise you to write back to them.

Thanks