My Trade-In Value was Changed

Please let me know who I can contact at Apple to file a complaint as this seems to be the only recourse I have in this situation.

First, we are end user like you. Unfortunately we do not have internal contact information that Apple have not published. Also in some regions Apple uses trade-in partners that are making the decisions.

There is no longer a way to electronically file a complaint regarding Sales, Service, or Support. Phone calls to giant corporations are next to useless. That leaves you the well-written business letter sent to Apple HQ.

For a decade I managed the customer service/complaint function for a firm in another product sector. I far preferred the business letter to finding a stack of "While you were out..." slips on my desk. Letters gave me time to investigate before contacting the customer and, were the matter a personnel complaint, the letter was hard data in my employees' permanent HR file at review time.

If you have a case number related to the trade-in, be sure to include it.

Many are no longer taught how to write a business letter. If your are among those, this is an excellent resource:

https://edu.gcfglobal.org/en/business-communication/how-to-write-a-formal-business-letter/1/

I would always recommend to take the device directly to the store for an immediate on the spot valuation. Any concerns with the screen would have been pointed out to you at that time and you could make a decision on what you want to do. "LCD display burn damage/streaks/discoloration across the screen" is such a broad category that it could actually apply to most screens, although you should have received pictures that noted the specific issue. Use this link to contact Apple directly:

Contact Apple for support and service - Apple Support