[Closed] Strange issue with Skype ..ideas?

We often speak via Skype to relatives in France. They have a Desktop PC upstairs but mainly use 2 Hudl tablets downstairs (which I gave them)
I also have a Hudl and they all run android lollipop which can't be updated.
The issue is that if either of us Skype's the other (ie international ) using any of the tablets , the caller audio cannot be heard. If they Skype family within France there's never an issue and if we talk using their desktop PC and our Android mobiles or PC ,once again all is fine.
So..the question is ... what's different about international Skype calling that could be causing this problem with the Hudl tablets?