tracking shows delivered buy buyer says not received

[rad_era_parts]

I recently sold an item and the buyer is saying they didn't receive it.   I mentioned to the buyer that I would have to open a USPS investigation and attempt to locate the package first as we can't just give refunds out on items that show delivered.  They did not like that of course.   The buyer has a hard time writing and spelling so it's almost hard to discern what they are saying.  What will Ebay do here ?  They have already left a negative.

Thanks

[soh.maryl]

Exactly what does tracking indicate?

And exactly what was the last estimated delivery date?