FedEx denied claim - what now?

So I recently sent in my phone for a warranty repair. It was repaired and was shipped back to me. However I never received the phone. I called HTC to inquire about it. They gave me the tracking information which showed that someone else had signed for it and that it was delivered to a receptionist. I live in a house so there is no receptionist to speak of. HTC files a claim (the items was insured for $500) and it gets denied. I ask why and they say to call FedEx as they have no information to provide me with. I call FedEx. They give me no explanation as to why the claim was denied and are unable to explain why a receptionist signed for my package. However, they insist they delivered it to the right address. Afterwards they tell me to sue if I don't like it. Is this my only course of action? Although it is clear that they mis-delivered my package, will I have trouble suing since I was not the shipper? Any advice is greatly appreciated.