2002 Buick Century o2 sensors

The check engine light comes on. It called for bank one o2 sensor. So I went ahead and changed both o2 sensors. I cleared the code and it stayed off until she accelerated hard getting back on interstate. I thought maybe it was a faulty sensor so I replaced them again. Same result. Other than that a great car. Please help, I went to three mechanic and they all charged me money, but couldn't help me.

So far I have spent $250 on o2 sensors, yet the code keeps coming back. One of the codes said something about the heater circuit.