Translation:Although they do not know us, they hate us.
Although the meaning is the same, your version may have been rejected because the clauses were switched, when there really isn't any reason to switch them. (Sometimes the English just sounds better when they're switched.) But I really don't see anything actually wrong with switching them here. You could try reporting it, since your version may just have been overlooked.
I typed in this exact translation, but it was marked wrong. Although they do not know us, they hate us.