cellular data does not work

Hi, my cellular data does not work. I have a week without signal...

When I try to enter to my cellular data it doesn't work and screen goes blank..so I can't even enter there to fix it.

Can anyone help me?

p.s. I spoke to my mobile operator they say everything is ok in the system. and I must have a signal.

So, I think it's something wrong with my iphone...