During the phone calls I I hear the sound of the other person very dark (deep, it seems to me with the lows too high) as if he were in a room closed with rumble. The same phone call without SoundSport Free feels much clearer.
Thanks for reaching out to the community and sorry for the trouble you're experiencing. Has this issue come up recently?
Can you please try removing the headphones from your phone, and clearing the Bluetooth paired list from the headphones and try to reconnect? Please press and hold power/Bluetooth button for 10 seconds to clear the list.
Please let us know how everything works out for you when you get a chance.