I returned an item Apple says they received a different item and shipped back (not what I sent), UPS says only apple can initate investigation

I returned an Apple product (42 lbs), Apple says they received a different item and sent it back to me which is not what I sent (this is 15 lbs). They said the case is closed. UPS has it on the record that what I sent is 42 lbs box but they wont open an investigation unless Apple initiates it.

Apple won't answer these questions:

- Why did they accept a 15 lbs item if the label says it is 42 lbs

- The box they sent back does not have any other label (including the label I attached) other than one label addressed to me

- Why do not they look into videos of what the UPS driver delivered to them so the videos will be tracked back to the ones in the UPS store that I drop the item at

In general, they are not willing to do anything just saying case is closed without any explanation. And as I said UPS won't help either.

My theory is either someone in UPS peeled of my label and attached it to a different box, or someone in Apple warehouse accepted the package and switched it. Please advise. This is $ 8000 (yes 8K!) item.