How do I remove a Collections Strategy from being 'In Use' so that I can edit the Strategy?

Summary:

I am trying to edit a Collections Strategy and associated Tasks, and in order to do make them editable they must not be 'In Use' - I have taken a number of steps to try to remove the strategy from use, but have not been successful.

Content (please ensure you mask any confidential information):

I am trying to un-assign a Collections Strategy from all Customers so that I can edit the strategy and strategy tasks associated with it in 'Manage Collections Strategies'.

I have used the REST API to close all Open tasks that are using the current Collections Strategy. I also amended the default Strategy in 'Manage Collections Scoring and Strategy Assignments' and ran the following ESS Jobs in Order: