Today, I was flying DEN-ORD-MSP. I missed my original flight and I was put on standby. The first flight cleared and when I got to ORD, the flight that I was on standby for was just about to start boarding. I noticed my name was not on the cleared list, but I was first on the standby list. Since there was only one gate agent, I decided not to bother her and just wait for her announcements.
She went through all five groups (1K through group 4) and never called my name. Then she disappeared on the jet bridge, closed the door and I saw that the jet bridge was pulling away.
When she came back out, I approached her and asked why I didn't clear. I told her that I noticed that there were a bunch of empty seats on the plane. She asked for my name and said: "Oh, I called your name a bunch of times but you never came. I remember, you had problems with your flight."
I told her that I never heard her call my name and that I was present throughout the entire boarding process; to which she replied: "Oh, I called you before all of that".
She then said she just put me on standby for the next flight and left.
I called for a supervisor and I explained the situation to him, and gave him the employee's name. He had another GA confirm me on the next flight, which left about 3 hrs later (and actually turned into a mechanical) and left it at that.

I am wondering if I've done everything I could or if I should have done something else. I am pretty mad about the whole situation, which made me 4 hours late.