You seem to have a concept of "existence" based on "substance ontology". (Aristotle). Later philosophers extended the meaning beyond the limits of "substance". Your "problem" is philosophically a non-starter.
i think that's a mis-fire response. Per my reading, the OP doesn't seem to be questioning the "existence" of "mathematical objects". The OP just implies that their existence is dependent on-, or interdependent with-, "physical things". Frankly, the question of "existence" isn't even raised.
The only sentence to which your response might
be relevant is the last:
Therefore, mathematical objects are not non-physical.
A double-negative that implies that the OP might not deserve the tired accusation of "realism", with which you so often abuse those that don't use your preferred lingo.
PS: If Aristotles's problems were actually a Φ "non-starter", given how much historical Φ information he provided and took into consideration within his own philosophical thought, we'd have much less philosophy than we do. In my opinion, without Aristotles's authoritative contestation, and Φ historical background, Platonism would be just another religion...