The letter was unprofessional. You're sitting here trashing Topps employees who are working to make a paycheck at (more than likely) minimum wage or just above minimum wage because you feel entitled to something.
The response you got honestly wasn't even half as unprofessional as the letter you sent. Lesnar WAS misspelled, and chances are good they have their inventory arranged alphabetically. The note with the misspelled portion was more than likely intended to make sure someone didn't waste their time searching for a Brock Lesner card for you.
I understand that you're upset with the way you feel they've treated you as a customer. Really, I get it. But, at the same time you're going to catch more flies with honey than with vinegar.