How do I delete a credit if I don't have proof that it isn't factual?

I am trying to delete a few credits of films that were wrongfully added to my page for years, with the request being denied every time. I understand you need proof that the credit isn't factual, but if I did not appear in these films then how am I to have proof that I wasn't in them? I have gotten credits removed in the past, so I don't understand why these few are giving me a problem.