freelander exhaust pipe

Hi good evening everyone. I have a 2002 freelander 1 1.8 petrol
i am having difficulty in buying the right part of the exhaust pipe. I bought the rear part about 18 months ago which goes from the tail pipe 2 boxes then meets the second part under the front of the doors and now the middle box is making a hell of a noise how ever the parts dealers say my exhaust should only be in 2 parts but mine is definately 3 pieces. the piece i want is around 1.5 meters long with a rectangular box about 12 to 15 inches long then a small vented round sleeve 3 inches long going to the bottom of the manifold coming from the engine.
does my car have a catalytic converter in one of the boxes as everyone says it should have and should i pay £270 for this piece.
its after market from dingo croft it also has some sort of sensor screwed into the top it is a oxygen sensor which must be taken out and reused in the new exhaust.
does this make any sense to anyone please help its a great little car but i have no clue in these matters and cant afford to buy a new vehicle just yet kind regards for any simple help Lester

Pictures of your exhaust might help, as it doesn't sound standard to me. The exhaust is made up of 5 sections. The 1st section is the manifold, which contains the pre-cat. The 2nd section is a downpipe, which connects to the manifold and goes backwards under the engine and rearward to a flange joint. The 3rd section is main cat is bolted to the flange of section 2. The 4th section joins the rearward flange of the cat, there is an O2 sensor near the flange, before continuing rearward through a long silencer, then bending under the LR rear suspension wishbone, where it terminates in a slip joint. The 5th section is the rear silencer, which joins the slip joint of section 4, before exiting on the RH side of the vehicle, under the rear towing eye.

Anything other than this arrangement isn't correct.