not Disturb not work

Hello,

I have an IPhone 4 updated to iOS 6.1.3; the issue I came across is the following one.

The DO NOT DISTURB function does not work; at first I set it to accept incoming calls only from family, but the phone would ring with any calls.

Then I set it "Allow Calls From NO ONE"; even so the phone keeps ringing.

So I am wondering if I have to reset completely my phone or maybe if the "Do Not Disturb" Function, simply is not compatible with a Iphone 4?

Or maybe there is some other setting to be done?

Thank you!