This is how i stop my service

Just like @inclement mention

But add `Service` to the front of your service name

from jnius import autoclass

package_name = "org.laner.lan_ft" # joining args from your buildozer.spec package.domain and package.name
service_name = "Mydownloader"
service = autoclass(f'{package_name}.Service{service_name.capitalize()}')
mActivity = autoclass('org.kivy.android.PythonActivity').mActivity
service.stop(mActivity)