If you want them to do something, reduce the size of your letter by 75%. Explain simply and clearly what happened and what you want them to do. Keep it simple.
1. You put a deposit down on November XX, promised delivery by Dec. 28. Do not use the term "Black Friday".
2. You repeatedly checked on delivery, never told that it was not going to be delivered until after Dec. 28. This prevented you from finding a comparable model for over a month, even though CC knew on Dec. 1 they were not able to fulfill your order. Your funds were tied up for an entire month for no reason.
3. You want CC to find a comparable model for the agreed-upon price because you were never notified that your order could not be fulfilled and they had your $520 for a month longer than necessary due to their lack of timely notification to you, which kept you from finding another model during that time. If they can't, you would agree to accept the floor model from your store along with the three-year service plan for the original price of $2599.
Now, on another topic. What difference does it make that the demo model was in use for a month? Does a $2599 TV have that short of a lifespan?