You used to be a challenge for her. You had a superior significance and she was irresistibly drawn to you. Now she's gone and you are saying: "I want my ex back!"
I am about to make a wild guess here, and yet is it that as time went on, you grew to be less and less of a challenge for her? And is it that currently, you're zero challenge for her? Not to mention that she believes if she wanted to, at any moment she could easily get you back again and twisted around her finger by simply saying the word?
Now I'm going to be a bit crude here, however as you know, to become a challenge again you need to demonstrate to your ex-girlfriend that her sexuality does not have any influence over you any longer. Contemplate what it's like when you're stalking her with not returned phone calls, voice mails, text messages, and emails. And after that consider exactly what it is like when you keep doing it (as many guys do) even after she's told you to stop. You are indicating to the woman that you're a low-value guy with no other choices.
Your sweetheart won't respect you again until you refuse her sexual dominance over you. Luckily you're doing that now by not directly communicating 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.
You should definitely stay 100% rigid with your communication cut-off. You should not be "pals" with her, simply because that rewards your ex with the continuing approval of power over you while supplying her a convenient reason to stay split up. (Your lover justifies that she's letting you down easy this way, assuaging any remorse she may experience.)
On the other hand, make sure to keep her locked in with the help of your stuff. In all likelihood quite a few your possessions are at her place, and vice versa. She may even owe you money as well. She could get a mutual friend of yours to ask you if you would like everything back again.
The ideal response to this is "No, not yet. The rationale is simply because her holding onto your stuff (and you possessing hers) is still locking you two in and ensuring future communication. You do NOT want to provide her the psychological closure that would result from settling your accounts.
For the next 3 weeks, you need to completely acknowledge -- and embrace -- the fact that you are an independent man now. Take what happened with your ex and learn from it. You've got a great opportunity to transform your life which will finally allow you to get your exgirlfriend back.