I'm thinking if you're looking more to learn self defense, you should think less about learning boxing and more about some kind of self defense course or martial art. Boxing's a bit finite on what you can and can't do. In self defense, well, there's no rules whatsoever as to what you can and can't do.
If you can find a good school that teaches Ed Parker Kempo, I'd recommend that. That branch of martial arts is very good for self defense. There are plenty of others that are good too and it's not all that uncommon to find someone teaching at reasonable rates.
Sorry to hear some jerk attacked you. Submission holds can be a real bitch to get out of. The best thing to do is try not to get into them to begin with. Good luck to you.