Ford KA radio code

Hello, I have a Ford KA from January 2006 and in order to change some parts, my friend had to disconnect the car radio... which no longer works. I went to Ford who asked me for 8 euros (not very expensive) to give me a code 5356, but it doesn't work. When I press 5 to validate, it starts a timer!!
I don't know how I can find the serial number because it's integrated into the car. However, when I press 1 and 5, some numbers appear, is that it? The number: 50702201
Can someone help me please?
Thank you in advance.