I would get the fault codes read again. I doubt if your car has 2 cat's.
Can you remember the fault code number?
Sound like a mixture problem to me. Could be a defective sensor or an air leak.
Continuing to drive with this problem will eventually destroy the one cat you do have.

Check all vacuum hoses around the inlet manifold for splits, cracks or blockage.
Check the exhaust manifold for leaks.
How old are the spark plugs? And the leads?
Spray a little water over the coil and leads in the dark. If you see or hear sparks then replace that part.