You were a challenge for her. You had a very high value and she had been irresistibly attracted to you. Now she's gone and you are saying: "I want my ex back!"
I am preparing to make a wild guess here, and yet can it be that as time went on, you grew to be less and less of a challenge for her? And could it be that at this time, you might be zero challenge for her? And also that she realizes if she wanted to, at any time she could get you back again and twisted around her little finger simply by saying the word?
I am going to be crude here, however as you may already know, to become a challenge once again you must show to your ex lover that her sexuality does not have any influence over you any more. Think about what it's like when you're stalking her with not returned telephone calls, voice mails, text messages, and emails. After which think of exactly what it's like when you keep doing it (as many guys do) even after she's told you to stop. You will be suggesting to the woman that you're a low-value guy with no other alternatives.
She will not respect you again until you refuse her sexual power over you. Fortunately you're doing that now by not personally corresponding with her. The last thing she needs to hear from you now is how much "I want my ex back", so stay away from her.
Be sure you stay 100% strict with your communication cut-off. Be careful not to be "friends" with her, simply because that rewards her with the continuing validation of power over you while providing her a handy reason to stay broken up. (Your ex reasons that she's letting you down easy that way, assuaging virtually any culpability she may feel.)
Then again, make sure to keep her locked in with the help of your things. Probably lots of your belongings are at her residence, and vice versa. She may also owe you money as well. She might get a mutual friend of yours to ask you if you would like everything back again.
The right response to this is "No, not yet. The reason is simply because her holding onto your things (and you holding onto hers) is still locking you two in and guaranteeing future communication. You do NOT want to provide her the psychological closure that would result from settling your accounts.
For the up coming 3 weeks, you must fully acknowledge -- and embrace -- the undeniable fact that you are an independent person now. Take what transpired with your ex-girlfriend and learn from it. You have a wonderful chance to revolutionize your life which will ultimately allow you to get your exgirlfriend back.