1) I'm at ABC College.√
I'm under ABC College. I'm with ABC College.
2) I'm flying with
vVirgin this time. √
3) I'm working WITH ABC company.
If you work for ABC, ABC are employing you. If you work at ABC, ABC are probably employing you. If you work with ABC, you and ABC may be collaborating on a joint venture, or you may be providing a service for them. Unfortunately, at and with are used fairly loosely, so you cannot be sure, without more context, what the working relationship between the speaker and ABC is. Even with 'for, we don't know whether the speaker is a permanent or temporary employee of ABC, or is providing a service for them.
Is the title appropriate? I've seen this somewhere. It's kind of common to use On + XXX as a title, isn't it?
Only if you are writing a paper about XXX. A better title for this thread would have been 'at/with/for' a company, etc?