Worst Day at Work I've Ever Had

I have been working at the same restaurant for 1.5 years and tonight was unusually busy and I was working with some slower waitresses. I work in a busy restaurant and some awful customers left a nasty note on top of not tipping on a $105.81 bill. I want to get in contact with them because I believe what they wrote is completely unfair and I would like to defend myself. I realize that it won't do anything, but I came home tonight feeling like crying because it was really hard not to quit last night after everything I had to deal with!

What happened? I'll try to keep it relatively short:

First off, at the restaurant we have no busser, host, cashier, food runner, nothing! Just the front and back crews, and we were short a girl to begin with. We have to do everything ourselves. A group of people arrived and we had no tables, so I put them on the waiting list. As soon as I saw an open table I bused, set it, and took the group to their seats. All within about 15 minutes. I got drink orders as soon as I sat them because I didn't want them sitting without anything to drink. After that I continued trying to seat people, all while running food, bussing tables, taking orders, cashing people out. I was trying to give everyone time and help, but it was particularly hard tonight.

I had the misfortune of seating the particular group in question and even got their drink orders straight away. At the restaurant we all share everything, and are not assigned specific tables, so I was not their assigned waitress, I was just one of the people helping out. Everything they asked me they got. I went past a few times asking how they were. Did they ask me for anything or complain to my face? NO! I was literally running through the restaurant, sweating like nobody's business, and was bright red in the face. I am incredibly hurt and upset that people would be that careless and rude to not say anything to my face, and call me out on something I couldn't help. It was crazy tonight. Every other customer in the restaurant was nice to all of the waitresses. They are the only ones. 

The only info I have about them are the type of credit card they have, the last 4 digits, last name, and first initial of first name. I don't think I will ever get to say what I was to them. I feel like so low right now. I am already going through a rough patch and this made me feel 100 times worse. I really wish I never got up this morning.