The call quality from my wife's IPone 6 is so bad. The call cuts in and out so that I can hear only the 2nd or 3rd word a lot of the time. The calls do not drop, we usually just hang up out of frustration. We have been into the store and the replaced the SIM card but that didn't help at all. What can we do to solve this? We feel like we are waiting our money paying for phone service when we can't make calls.