isn't there a law for that? as things become cheaper you consume more?
You're probably thinking about jevons paradox. But you slightly mis-stated. It is the phenomenon that increasing the efficiency of resource consumption can end up increasing total consumption.
As you stated it, it would merely be a property of (nearly) all demand curves. Jevons paradox only happens sometimes. It isn't a law.
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Jevons paradox: https://en.wikipedia.org/wiki/Jevons_paradox
Jevons paradox.
jevons paradox