Cell phones: Motorola C155 directional problem

Motorola C155 directional problem

My tiny company uses prepaid cells to cut costs. It works; cuts idle chatter way down. One of our phones is a Motorola C155 from Net10 & recently it has developed a problem where unless the user is in exactly the right spot, facing the right direction, we can hear the person on the other end, but they can't hear us, & often we must shout to be heard at all, & then it's very faint. Yet, when in the right spot & facing the right direction - whatever they are.. they vary - normal conversation happens.
Net 10 is about useless for help & you don't want to talk on the phone with their help people.. endless repetitions of how sorry they are, & not much help or they screw up the phone completely. Took out over 200 names from the phone book once, by hitting a wrong key on their end while trying to fix whatever was wrong that time.
We think of changing, but the number is advertised all over and there's the phone book - how to transfer it? 200 entries will take us forever.
Does anyone know of a software code that can be input to update the phone software so the spot/direction problem is solved? We had this problem with our Verizon phone & they gave us a code to input monthly & the software is updated & our problem is gone with that phone.