@Supie-Chan you can't just "try", its not easy but you have to be confident and assertive, if you only "try" to defend yourself and fail to actually stand on business people will only respect you even less and clown you for it.
I know it's harsh but that's just bullying works, this situations is terrible but it seems your on your own so your gonna have to toughen up if you actually want them to leave you alone
I think before you handle them you should work on building self confidence, i know it sounds hella random but maybe try working out or boxing workout routines so you're more confident about your physical strength and ability to defend yourself so when you ARE assertive it's more genuine (theres many boxing workout videos that you can do for free without equipment, some are as short as 10 minutes long if you have a busy life.)
Like i said im not trying to be harsh, but as someone who's gone through the same thing (except for that creep situation you mentioned) all that "ignoring" and "tell the teacher" stuff doesnt actually fix anything and you WILL have to assert yourself properly if you don't want to be pushed around your whole life.
it's scary at first but most people wont actually fight you over it and even if they do (and you do lose), they'll likely leave you alone after just because they know you're willing to actually fight them in the first place.
As soon as I started cussing people out most of the conflicts I had stopped, but you have to ACTUALLY be confident and GENUINELY assertive, don't be afraid of these losers who think they're the shit.