If a subscribers is able to themselves choose to deactivate their account make a smoth integration that stop the recurring billings aswell. Most apps programs you download have a trial period but there is a connections to the billing and after the trial period is over the recurring billing is activated however if the subsriber ends the trial period then the billing will end at the end of that trial day or month. This is to ensure smoth and automated customer experiend. You can test it out on paid app on appstore . There is also a place on the phone where you can see all the memberships you have used but stopped in advince and are not paying.