Thank you very much for your post.
Peter I cant find list of the product`s inventories, even if click green icon.
Have you created more inventories? Can you upload the screenshot of the product, please?
Peter NOTE: When change to Pending Payment status the stock quantities will give back to the product automatically. You can check the stock quantities changes in the Order notes or going to the inventory tab in the product page.>
You are changing from processing to pending - both do not change inventory amount. You need to change from pending to completed or another way around. This is actually a WooCommerce function and I recommend you read the WooCommerce documentation too, pls.
Hope this helps.