It appears you have a long way to go to repair your reputation.
For starters, I would suggest listening to your customers and taking care of their needs rather than arguing and finding fault with them - your attitude will either help or hurt your business.
For instance, I rarely deal with an eBay seller that has less than a 99.4% positive rating (that is about 199 happy customers out of every 200) - why?, because to me that is an indication that the seller has issues that may affect my serenity if I do business with them.
The only thing that you can control is how you react to this situation. If you continue to react this way you will have negative results. If you learn from this situation and treat all (as in 100%) of your customers with dignity and respect, you will have positive results. It is all up to you.