How to unlock firmware-locked 2014 MacBook Air with proof of purchase and AppleCare?

My computer is lock, looks like firmware, however it was purchased in 2014 and neither my credit card or merchant have copies of my receipt. There records do not go back that far and I did not keep copies either since retention period to save was up. I purchased a new computer and Apple helped me migrate the information. So it is my laptop, plus I have proof that I also purchased the Apple care the same day I purchased the computer. What other proof do I need..

[Re-Titled by Moderator]

Original Title: Fireware lock