rake db:rollback not working?

Solution (see my comment): run

rake db:migrate:status

and correct problems you find there. In this case (per @MarkThomas' followup), you might want to check all files you need are in place.

This is what worked for me. Combine the steps given in this answer and comment by dB.

1. run rake db:migrate:status
2. If you have a ****NO FILE**** entry, just note the version number as noFileVersion. Note the version of the entry just above no file entry(stable_version).
3. created a "dummy" file with name noFileVersion_create_nothing.rb, and body

class CreateNothing < ActiveRecord::Migration 
  def change 
  end 
end

4. run rake db:migrate VERSION=stable_version
5. remove the noFileVersion_create_nothing.rb manually.
6. run rake db:migrate.
7. run rake db:migrate:status again to check if No file entry has disappeared.

The following worked for me: rake db:migrate:down VERSION=20190304092208

Version number can be obtained by the following command: rake db:migrate:status

This was the last version number to rollback one last migration