Something wrong with my Galaxy S4 speakers?

My Galaxy S4 for some reason is glitching from the speakers. Whenever I try making normal calls, the speakers work as well as the ones you put on by your ears. Basically I can hear the person I'm calling. But whenever I try making calls through apps such as Tango, Viber, or Skype, I can't hear anyone, but they can still hear me. I can, all though, BARELY hear them when I put the spot where you charge the phone close to my ears, which I don't understand why…

The phone use to work perfectly fine with all three apps, just recently it did this.
The phone has NEVER been dropped in water.
All the volumes on the settings are on max.

Please, I need a solution. I've called Samsung and they wont help me because they say this is a problem with a 3rd party (the apps).

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