fan constently blowing hot & cold - Fabia 1.9Diesel

Hi Guys, 

I've looked through the forum but didn't seem to find an issue similar to mine - sorry if i missed it. 
I've got a Fabia Mk II 1.9Diesel. 

For the past month the fan keeps on blowing on the sides and the blowing noise is present all over the cabin. Here are some indicatin of the issue: 

* the temperature control is working. So i can choose whether i went hot or cold air to be blown 

* the speed of the fan is not working. Even when turned off, air keeps on coming out from the side vents. Only the central vents are controlling with the fan speed button. 

* pressing any buttons, i.e. auto, recirculation or anything similar does not help 

* for some reason the intensity of the fan changes with vehicle speed ( seems to get quieter above 50kph) and worse when reverse. This might just be a 'lucky coincidence' but the intensity does seem to drop everytime i'm on a highway. 

Any thoughts are welcome. 

Thanks :)