I have deleted a feed from Auto Blog but it is still posting blog posts from the source.
It is similar to the problem described here: https://premium.wpmudev.org/forums/topic/autoblog-continues-to-post-feed-content-from-deleted-source
I tried deleting the plugin and reinstall again and it stopped the issue.
But this cannot be a long term solution because I have already created a few feeds that I want to keep. Only one feed that is not needed was deleted but Auto Blog still keep posting.