Non response from cutomer service complaints dept.

It's been 4 weeks now waiting for promised phone calls or emails from a manager at the customer service dept to respond to my complaint. I have had to phone in many times asking for a response, they promise to call the same or next day, they don't call. I believe they know they are in the wrong and are avoiding the issue. I have been a customer for over 25 years. I am disgusted with this treatment.