would it be correct for me to say "não é de vocé?" I don´t know how to type the accents on my keyboard yet so sorry for that I think you will get the point anyways.
You can say that, but it has another meaning. "Não é de você" = "thats not about/of you". Its not yours = não é teu, tua, seu, sua.
If you are sure you do not have any extra accidental key strokes and it is exactly the same, report it. I typed it in and it was marked correct.
Because when you don't have a pronoun in Portuguese you usually use "it" in English.
- it is not yours = não é teu/tua/seu/sua
- she is not yours = ela é tua/sua.
I wrote "No it's yours " and was marked as incorrect. I think the context can be easily be confused, so it should accept this other interpretation. Don't you think?