Xperia Mini/pro :: SK17a Is Not Switching From Headphones To Built-in Speaker?

I bought my Xperia SK17a a few months back in Vancouver, I then moved to Mexico, I unlocked it here in Mexico and it has always worked fine except for one thing: when I plug in my headphones I can hear my media just fine, but then if I unplug them the phone won't detect that it no longer has the headphones and so the sound and media will keep playing as if it the headphones were still plugged, obviously I can't hear nothing coming out from the built-in speaker because it keeps sending the sound to the 3.5 mm jack. Sometimes I can make it work, this will only happend if I shut down my phone or if I slightly plug in my headphones on the jack but not enought to get the music , after I do that I can hear a constant "tap-tap-tap-tap" as if someone was knocking the door, however I can't always do that or it dosn't always works. I can also hear that "taptaptap..." sound when I record or make a call and have the built-in speaker working, such speaker stop working the second I plug in and out my headphones and if I record a video with the headphones plugged or the speakers not working I can no longer hear such tapping on the video. Also, if i plug in the headphones I can no longer hear anything during a call, but they can indeed hear me, If i want to hear the other person I'd have to plug in my headphones or pray for a miracle to happen.