Appeal on overpunishment for exceeding word count was denied – how to proceed?
Accept it and move on.  Consider:


You had a clear rule for the word count
You violated that rule
You appealed and were denied


And that's it.  Engaging in other extreme forms of behavior, such as trying to involve a lawyer (!), will surely sour the attitude of everyone involved toward you.

To address one point specifically, when you didn't hear back from the professor about word count rules, you should probably have defaulted to following the rules to the letter.  I personally try to always respond to the emails I get, but I admit I vastly deprioritize emails that are asking me things with clear answers already available - such as a word count limit.