Surprised this wasn't mentioned, but if you log into RS in SSMS (windows Authentication only), you can stop the job there. Expand the Jobs folder and it will show all the current reports running, which can right click and stop. Among other things. This also avoids deleting the subscription, which probably isn't the best answer.
Thom~
Excuse my typos and sometimes awful grammar. My fingers work faster than my brain does.
Larnu.uk