Can someone teach me or give me some advice about self defense?

I'm so serious about this matter, I feel unsafe these days because I came home late because of my deadly schedules (like from 7 in the morning up to 9 in the evening da hell) and for thesis writing (I came home at 12 midnight, sometimes) And some drunk man or he's in a dip because of drug, wants to harm me with his knife but thanks for my umbrella, I hit his face so hard and I ran as fast as I can. That self defense is not enough for me to face those kind of people..... 

And a while ago, someone prank me on the phone about my mother was engage in accident and the fck I almost killed myself for giving my cellphone number (but nah I burned it and threw it right away) okay you can blame me for my stupidity but my mother was mentioned of that fcking human being! They want me to come at the place where my mother was located. I almost cried when they said that but I noticed that it wasn't my mother that I'm talking to the phone, and that's it! Kidnapping was famous here in our country (sad to say) and I almost fell in that trap!

Because of that incident, I decided to stay here in my house, for my safety of course. And I'm scared because I can't avoid that kind of situation because of my classes until night... /sighs hard/

Any advices you'll give are very important to me. Thank you in advance, and please keep safe!