Why I can't answer calls.

I have a Samsung J5. When I get incoming calls, I slide the answer button and it looks like the call is answered but then it goes back to the answer rejects screen. I can make outgoing calls and the rest of the phone is fine. I used my land line to phone my phone and there is no ringing tone from the land line ear piece but my cell phone rings and then have the problem as above. Please help it is driving me crazy.

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