If every other business has taught them that this is the only way to deal with things and that actually going through the "official" cancellation procedure is next to impossible (and an opportunity cost besides), I don't see how you can ask them to stop doing it.
It's apparently a strategy that works, and just because it's inconvenient for you doesn't make it their obligation to stop.
It's apparently a strategy that works, and just because it's inconvenient for you doesn't make it their obligation to stop.