What an experience. You are describing a series of unusual yet inexcusable mechanical delays.
I frown on the profound and worsening lack of resources in airline customer relation departments. That being said, it is extremely rare for any airline including Delta to take more than 50 days to respond to your concern. These departments generally provide some form of compensation for a single mechanical delay (e.g., your $100 voucher). If your entire series of issues can be validated against their flight records, I would assure that you will receive significant compensation.
First: If you contacted Delta electronically, including their website, I suggest that you check your junk/spam folders to ensure that a response has not already been received. You may also wish to check your frequent flyer account to see if any bonus miles have been added. Look for something like “Customer Relations Bonus Miles” or “Service Recovery Bonus”.
If you don’t find anything, print out your letter and send it via Postal mail. Their address is on the right hand corner of this page:
https://www.delta.com/legal/delta_cu...ment/index.jsp .
You need and deserve a response, so don’t give up—and keep us posted on what happens.
Matt