I'm stuck with a classic M&M problem that many of you will recognise. Four letters regarding a UA flight that didn't credit have taken us full circle from boarding passes being submitted but mileage credit rejected ("already credited to another FFP"), through two iterations of "boarding passes you have submitted twice do not suffice [...] also need a copy of your ticket or passenger receipt", back to "ticket you have provided does not suffice [...] also need your original boarding passes".
Is there any sensible alternative to giving up?