Stop sccm task sequence deployment

It may unfortunately be too late. Once the clients have picked up the advertisement they're going to attempt to pull it from the distribution point.

Assuming you've stopped advertising the package to your clients by removing them from the collection or removing the advertisement itself, you could prevent an individual machine from thinking it needs the update and thus stop it from downloading it by running the Application Deployment Evaluation Cycle from Configuration Manager on the workstation. Obviously that's not particularly practical across 10,000 machines.

If you want to be drastic, you could probably find and delete the package from any distribution point(s) which would theoretically stop network traffic, but your clients may get quite angry about it - I'm not sure how the Configuration Manager client handles a package disappearing mid-download.