Steel cooker is not a Faraday cage?
To be a good Faraday cage, an enclosure needs to be completely sealed, with no gaps larger than about a tenth of the wavelength of the radio waves you want to keep out.
Microwave ovens have a tightly-fitting door, and a metal mesh in the door where the window is.  But even they won't completely block a mobile phone signal.
A normal domestic oven may have a glass window, which would let the radio waves in.  Even without a window, they have loosely fitting doors with rubber seals, and rubber won't block a radio signal.
See also This Physics Stack Exchange question.