Hey Shazil thanks for the question.
I actually just went through this process because I was deleting outdated products and adding new ones to my store. When you delete a product in Oberlo, a popup will appear asking if you'd like to delete it in Shopify as well. You must check this box to make sure it is deleted in Shopify too. Otherwise, it will continue to exist in Shopify.
For the previous products you tried to delete, you will need to check them in your Shopify Products page and press actions > delete. Hope that helps!