Peugeot 308 engine cooling fan keeps going everytime i switch the car off

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Hello, Can you please help I think something maybe seriously wrong with my Peugeot 407. If I drive the car for 5 mins or more and then turn off the engine the front fan keeps going for 15mins approx to cool the engine down. this happens everytime. It doesn't seem like its regenerating. I get a depollution fault everytime i turn on the ignition. I don't see much exhaust smoke coming out of the exhaust pipe, but there is heat coming from it when I turn off the engine. I have taken it for long 60min drives in 3rd gear at approx 60mph to try for a forced regen but its not working. I have also noticed this morning that the heater lines in the rear window are coming on without even pressing the button. Can someone please help me, I'm pulling out my hair trying to figure out what to do. I just feel like I want to get rid of the car altogether as its given me nothing but bother. Please help. Regards, Jerome