Mazda Repair: 2001 Mazda 626 cel code P0133, oxygen sensors, o2 sensors

Question
I am trying to get my car to pass emissions. The CEL was on with the code P0421 for the second year. Last year we replaced both O2 sensors.  This year we went to a shop and they said it was the the catalytic converter (the one closest to the motor). Went a head and had it replaced plus both oxygen sensors.

Now we're getting the CEL code P0133. Replaced the O2 sensor before the catalytic converter again, thinking it was defective. We're still getting the code.

Not sure what else to try. Help?!?

Answer
code is saying o2 sensor circuit, slow reresponse cycl ban no.1, sensor no.1. not all o2 sensor codes indicate a bad sensor. normally it's never the sensor unless damaged it's the preformance of the engine producing to much emmisions. and it could be for a number of factors. have a garage that knows how to properly dianose codes loo at the car sounds like whoever your taking it to is just changing parts hoping something will work.

also remember you have to clear the code after the repair was done it doesn't clear on it's own