It’s fairly standard to hear creationists say that evolution is “just a theory” as part of an effort to discredit it, but that entire argument involves ignoring the very concept of what a scientific theory really is:
How many times does this have to be explained?
A scientific theory is not “just a theory”;
‘A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment. Such fact-supported theories are not “guesses” but reliable accounts of the real world. The theory of biological evolution is more than “just a theory.” It is as factual an explanation of the universe as the atomic theory of matter or the germ theory of disease. Our understanding of gravity is still a work in progress. But the phenomenon of gravity, like evolution, is an accepted fact.’, American Association for the Advancement of Science.
Also a scientific law differs from a scientific theory in that a scientific law does not, unlike a scientific theory, propose a mechanism or explanation of the phenomena under consideration. Therefore a scientific theory is a more powerful tool than a scientific law because the law can only be applied in specific cases and does not offer any explanation for what is happening. eg Newton’s law of gravity gives us an equation to calculate the attraction between two bodies but gives no explanation of why the equation works; and as we know Newton’s Law does not actually hold when applied outside the boundary conditions for which it was created, which is where Einstein comes in.
The problem with arguing with creationists, of course, is that they clearly don’t perceive reality as you and I do. They live in an alternate world where facts are fungible, and they always will.