I am getting a persistant P2626 code after replacing the 02 Sensor

I have a 2005.5 Volkswagen Jetta 2.5L engine code BGP. My check engine light came on a little over a year ago and it ended up being a P0420 code. I took in and was told I needed a new catalic converter. I had it change. A few months later the check engine light came on again. I took it once again to a mechanic and was told it was a P2626 code and the bank 1 o2 sensor needed to be replaced. I replaced the sensor and a couple months later the check engine light again came on. I connected a scan tool and it was again a P0420 code. The catalic converter I had changed a year ago was under warranty so it was again changed a month ago. A few days later the check engine light once again came on with a P2626 code. I reset it then a couple days later another light with a P0420 code. Reset again a day or so later another light with a P2626 code. Now over the last month the light has been on and I continue to reset it every few days and the P2626 code is the only one that comes up. Any advice of the culprit of the problem would be greatly appreciated.