Get Back Your Ex-Girlfriend By Being Less Available and More of a Challenge

You were a challenge for her. You had a high value and she was irresistibly attracted to you.
And I'm going to make a wild guess here, but could it be that as time went on, you became less and less of a challenge for her?
And could it be that right now, you are zero challenge for her? And that she knows if she wanted to, at any time she could get you back again and wrapped around her finger just by saying the word?
I'm going to be crude here, but as you know, to become a challenge again you need to demonstrate to your ex that her sexuality has no more control over you. Think about what it's like when you're stalking her with unreturned phone calls, voice mails, text messages, and emails. And then think about what it's like when you keep doing it (as a lot of guys do) even after she's told you to stop. You're indicating to the woman that you're a low-value guy with no other sexual options.
She won't respect you again until you refuse her sexual power over you. Fortunately you're doing that now by not directly communicating with her.
Make sure you stay 100% strict with your communication cut-off. Do not be "friends" with her, as that rewards her with the continued validation of power over you while giving her a convenient excuse to stay broken up. (She reasons that she's letting you down easy that way, assuaging any guilt she may feel.)
However, make sure to keep her locked in with your stuff. Most likely a lot of your possessions are at her place, and vice versa. She may even owe you money as well. She may get a mutual friend of yours to ask you if you want all of it back.
The best answer to this is "No, not yet." The reason is because her holding onto your stuff (and you holding onto hers) is still locking you two in and ensuring future communication. You do NOT want to give her the psychological closure that would come from settling your accounts.
For the next 3 weeks, you need to fully accept -- and embrace -- the fact that you're an independent man now. Take what happened with your ex-girlfriend and learn from it. You've got a golden opportunity to revolutionize your life.