Most companies have at least one Customer Relations Officer. For no apparent reason, most of those companies don't train them. If you come to them with a complaint, it can often escalate into a full-scale argument. It might be helpful if I explain how I used to train my staff.
When a customer comes to you with a complaint, he/she is like a balloon full of hot air, frequently angry, unreasonable and generally difficult to deal with. This is what you do;
Say "I'm sorry you've had a bad experience. I'd like to hear all about it. If you've no objection, I'd like to write/type/record what you are saying to ensure that I don't miss anything". Then shut up!
If they are physically with you, try to look interested. On no account interrupt or argue, even if they are talking nonsense or saying something you profoundly disagree with. Every time you interrupt, they fill up with hot air again. If they can get through their entire narrative without interruption, they have become flat. All the hot air has gone and they are reasonable people once more.
When you then start to address those things you disagree with, say "I can entirely see your point". Don't follow that with the word "but". "But" is an argument alert. Say something non-confrontational, like "have you considered.......", "is it possible that......". Then gradually lead them to the point where you are both in agreement.
You then tell them that you are passing the entire case up to senior management to determine what action will be taken. Give them a time-scale in which the matter will be resolved and make sure it is adhered to. The customer will leave the encounter with the firm belief that their problem is being taken seriously and addressed.
That wasn't difficult, was it?