2002 Toyota Corolla after market catalytic converter proble

2002 Toyota Corolla Front Wheel Drive Automatic 96000 miles

I recently had my car diagnosed and found out my catalytic converter was bad and I needed a new one. So I told Complete Auto Care to fix my car and do what they needed to do. The next day my check engine light came back on. So I took it to Auto Zone and they told me it was my catalytic converter. I was like what I just got a new one! So I took my car back to the shop and he put it on a machine. Next thing he does it looks under my car (at the catalytic converter) and says oh heres problem. He said that I did not get the manufacturers part and it was an after market part. He said some Toyota's will take the part and some won't. He also said that the reason my check engine light was on is because the catalytic converter they put on is bigger than the one that is fitted (manufacturer) and it is causing the 02-sensor to read wrong (I have no idea what this means). Anyways my car has been burning gas like crazy I have to fill up twice a week now. My car also has been vibrating alot harder. I spoke to the manager of this shop and she told me it would cost another $200 to get the right part.