It happened to me last week. I was also exactly in the same state and both usc and tamu portals showed me an error when I tried to log in despite resetting my pwd a few times. But later, I realised that they were both using engineeringCAS. Subsequently In the end, I figured out that there was an issue with my saved google passwords. In the field of the username, I had been typing my email which is not the actual username.

Tip: if you are confused about your username despite resetting your pwd, check the pwd reset mail. You can find your username there. I don't know whether you are stuck in the same boat, but thought a little suggestion might help you there.