There are many words which take a very different meaning in their scientific context to what they might mean in everyday use.
Among these is “law”. When we talk about a law of science, we don’t mean “one of the strongest rules of science”. A law is simply a (often mathematical) description of something that happens. The law of conservation of energy (or mass-energy for those who are learning about mass-energy equivalence) is: “energy cannot be created or destroyed, only transformed.” Mathematically you can write that same thing as
ΔE = 0
It doesn’t tell you how the energy is conserved or transformed or anything, just that it is. (You’d need a theory to explain the mechanism!)
Laws can be changed. Laws can break down or fail to apply under particular unforseen circumstances. For example, Newton’s Laws of Motion are incorrect when you start comparing things moving close to the speed of light relative to each other, but they are still laws… they just don’t apply under some circumstances.