Echo on my mobile line.

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I can hear echo on my mobile line for a long time,i cannot explain why this is so but it was so trerrible that i started to feel someone has tapped my line or something.I can hear my voice been repeated almost twice or so,what do you think can cause this? Initially,i thought it was the location that i was but later i changed my location and it was still thesame. I want your solid contributions please.