Problems With sound and Mic

[igud]

Hi,

I have used Fongo for the past few years on my old Sumsung Nexus phone and it worked great.
Last month I got a new phone. it's a unlocked T-Mobile Optimus F6 d500 phone. And now I'm having trouble with Fongo.
The fongo app works the first time I use it, (each day or if I turn off the phone) but after that I can dial and receive calls but the sound does not work.
Any idea's to fix this?