I can see both sides here. On the one hand, he may really not have gotten any missed-delivery notices from the USPS - my postman here is great, but in places I've lived previously it was a horror show of mail going to the neighbors, not delivered at all, etc.

On the other hand, I notice that both attempts were right around Christmas. It's possible he was gone when the first and second notices were left, didn't bother to do anything about it when he got back (or was gone too long), and now is claiming that he never got them at all.

No matter what you do, I'd brace yourself for a negative feedback.