What makes you think it is still running?
If that assumption is based on it not beeping it won't as you've killed the thread it was running on instantly.
Perhaps if it's a slow running task and you are saying things happen after you kill and disable it might be the UI (e.g. activities in your file manager) catching up with underlying events that happened before you stopped the task)
If you can give more detail as to why you think it's still running that would help us diagnose.