Smart meters can be turned off remotely for bad debt(or for any reason the supplier sees fit), just as a normal meter can be turned off and isolated manually for bad debt.
They are not allowed to just switch them off and certainly not without a very good reason. There is no practical difference between the process of old meters and Smart Meters, other than that they can remotely switch SM's off, rather than sending a guy round to cut the supply.
SM are better able to withstand energy thieves, in that they have detection circuits and can phone home is interfered with.