Azure DevOps Services: purge a file from pull request history after a history rewrite

We committed a file containing personal data to an Azure Repos Git repository and merged it through a pull request. We have since rewritten the history and force-pushed, so no branch or tag references the file any more. The original commits are still reachable through two pull requests: one completed, one abandoned.

How can we have the original commits and the file permanently removed from the service, including the pull request references and their diff views?

We can share the organisation, repository and object IDs privately with a support engineer.