person phoned can not hear me (using Imac)

[alwl]

Originally when I received my new number this time I could call out and the freephoneline worked. Then somehow 2 weeks ago I could hear but the other party could not hear me. So Fongo told me I had a mix-up and when I re-registered I got the number from my freephoneline that I had a year ago [but that had stopped working during the change-over] so I cleared all the files from Desktop and rebooted my Imac and re-downloaded the APP and no change. Using the OLD number I could call out but nobody on the other end could hear me. So I went through the same procedure yet again; still no luck. Today I tried going into the HD Library but did not find anything to throw out ... is there something that I'm missing?