I hear myself twice on internet voice call

hello,

I am using Teamviewer 12, on windows 10 home . not laptop.

I am use Pantronics headset with mic model 478. whean I want to make a internet voice , i turn off my speakers and uncheck computer sounds in teamviewer toolbar. 

the other person also use his iPhone earbuds or headset with mic, he can hear my very well and I hear him very well , but I keep hearing myself twice on my headset and I can't work like this.

how can I fix this problem?

thanks

Hilla