Phone only showing one bar and drops calls

Doesn't matter if I'm making a call or answering a incomming call the phone just drops the call for no reason. All the bars may be lit up like a Christmas tree. Then "POOF" there out and the call gets dropped.The phone is a Boost Mobile factory refurbished model. I've only had it for two weeks. Please any help with solving this problem would be greatly appreciated. Thanks... could it have something to do with the antenna? or some setting I missed ?