Why do my microphone and speakers not work during calls?

Hey guys,

i bought an iPhone 5 but one function does not work. Only during calls my speaker on the top, my loudspeaker and my microphone do not work. I can't hear anything what the other person says and the other person can't hear what i say. Neither the normal speaker nor the loudspeaker works during calls.

I replaced the lightening connector and the speaker but it doesn't work.

The weird thing is I can use Siri and other apps where the microphone is used. Moreover I can listening to music with my loudspeaker.

So those things do only not work during phone calls.

But I have a signal and I can call people so that it rings and people can call me so that my iphone rings and I can accept the call. Only problem is that we can't hear anything.

You have an idea?