No service or emergency only

i have an unlocked l6 using t-mobile. the phone works good early in the day then gradually gets worse. it will say t-mobile screen and and i cant recieve calls and if i do it hangs up when i answer. if i text or call it says call failed or unable to send. when it was fine a half hour before.i put it on the charger and it says charge complete. it gradually goes from t-mobile to emergency only to no service it is quite frustrating because i like the phone. one more thing ive called t-mobile and they say it is not on there end and ive put my sim in other phones and it works fine please help before i through this phone out a moving car.