I've been told that there are there two catalytic converters in the Elantra 2003

What is your question?

First I had the flex pipe changed, three weeks later the engine light came on and I was told that I needed a new O2 sensor, I had that done, now the engine light came on again and it's indicating that catalytic converter is bad. I've used the product "cataclean" (placed in with 1/4 tank of gas or less) twice and the light came back on first after 25 miles, second time after 29 miles. Now I'm told that I have to put a new converter in, 15 year old car with 134,thousand miles. Car runs great! No other problems, doesn't burn oil, trans is good. I hate to put anything else down for fear of jinxing myself!! I was told that there are two converters in this car and that it's also rated for the Calif. emissions codes. Which is the more costly model.

How long has your 2003 Hyundai Elantra had this problem?

Since last week, after the 02 sensor was replaced.