OP, since you are at the AC and have the time, you should be able to ask the agent at the desk there to print out your PNR. You may want to also ask if your original flight went out full.

There should be a time stamp on the PNR which confirms the time you were at the gate based on the GA rebooking your res. Depending on the actions of the gate agent, and the record, you could request IDB compensation. If the flight went out full, this may not be possible.

The GA probablly also thinks they scored by getting you to pay the SDC fee. Is the flight the GA confirmed you on full? If not, why pay the fee? The agent at the AC should be able to answer this. Based on your status and the number of people standing by for the flight, you can get listed and have the charges reversed.