Tone of my message is doing the the job I want it to. As to being upset, not untill I read your last message. Being that I manage customer service call center's let me re-write your message for you so that perhaps, you can dissolve an angery person much quicker with less words in the future;
"I apologize for the typing error of your name. I understand that you are upset and allow me the chance to clearify a few issues. Records due indicate that a note was sent to you however there may have been an issue with the grader releasing that message to allow you to see it. We having taken steeps to resolve that from happening in the future. We do indeed have your assignment and it will have it graded with in the 7 - 10 buisness days for you. Although I understand that this issue can be troubling and can cause emotions to run high, please make sure that we keep our discussions on a proffesional basis."
See how much less words that is and it doesn't put a person on the defense in the first couple of sentences?