Read the lease. It may well say they can do exactly what they are doing. I believe I have heard of this happening to others.
You might also review what the lease says you would have had to pay to buy the vehicle at the end of the lease. Was it depreciated original cost, or current market value, or something else? The current market value of used cars is sky high.
If the contract says they could have charged you fair market value, they had a reasonable expectation of receiving that at the end of the lease. It is certainly harsh to make you pay it, but maybe not totally unfair.
I had a vehicle leased and it was destroyed in a hail storm. Called the leasing company and told them where it was and that the insurance co said they would pay full retail used car price. Guy said, well, you won’t get hurt too bad. I pointed to paragraph 56 or so wherein it said the company would accept insurance payment in full for acts of God. Guy said I did not know that was in that lease. I responded it is, you got the news of where it is and one more thing, the Ford place said they start charging storage tomorrow, click. Never heard a word again,