When we are trying to delete the content type we are getting the below error.
Another site or list is still using this content type. If you would still like to delete it, please remove the content type from all sites and lists and then try again.
In my case I already deleted the list, but still I am facing the same error message. The same list is available in the recycle bin, follow the same steps as per the below.
Delete from site recycle bin.
Delete from Site Collection > Site Settings > Site Collection Administration > Recycle Bin.
Delete from End User Recycle Bin Items.
Delete from "Deleted From End User Recycle Bin."
Now you can able to delete the content type successfully.