That's exactly what I did last night.

A rep emailed me back today and apologized. Turns out the return trip departure time changed as well, which she also apologized for.

She said that she passed along the information to their "Schedule Change team" and that their records do show that a mistake was made in not contacting me.

Now I am satisfied. The most important part of customer service to me is when they acknowledge "we made a mistake, and know about what mistake was made and will avoid it in the future."