Issue with fans working overtime

Hi,

I have an Octavia Vrs 2001 and she has an unbearable issue which I have been trying to fix for the past month or two. Basically when i put the key to on position both fans fire up full speed and they never turn off as long as the key is in that position. When removing the key, no matter if the car was driving or not, the fans sty on for around 10-15 minutes. I went through the climatronic diagnostics to check all the temperatures to see if any of the sensors have failed, I checked the fuses, checked if any wires got messed up, and a buddy lent me a working fan controller to swap it and see if that was the issue. I had no luck so far so since I read this forum a lot I thought someone here might have an idea whats happening. Cheers.