You may think the abstract structures that you learn about are fixed fundamental truths, but just read Lakatos’s account of the multi-decade debugging of the Euler characteristic for polyhedra and you will realise that maths is both created and discovered.
How do ya like them apples for yer epistemology!
Another example would be limits vs infinitesimals - which is the “true” foundation of calculus? [1]
Or have you ever struggled with the Axiom of Choice?
[0]: https://en.m.wikipedia.org/wiki/Proofs_and_Refutations
[1]: And the correct answer, as all you Coventry City fans will know, is: trick question