In do not disturb option what does repeated calls option mean

The repeated calls option means that two attempted calls from the same number less than 3 minutes apart will over-ride the do not disturb settings and ring through. The feature is intended to allow for callers who are not on your "allowed list" to by-pass the do not disturb settings in an emergency should they need to reach you.

So, for example, you may not have your employer in your allowed list of callers, but if they call you twice in less than 3 minutes, their call would then go through. It is effectively a "persistent" caller option.

Please explain what you mean by "second incoming call not received". Do you mean that if you are on a call and another call comes in to your phone you do not have the option of seeing it or answering it? If this is what you mean you must contact your carrier and ask them to enable Call Waiting on your account.

Do Not Disturb is not related to your question. When Do Not Disturb is enabled only calls on your Favorites list will ring. All other calls will go to voicemail. If you enable 2nd call then ANY number that calls you twice in a row will ring the 2nd time.

The Silence feature has 2 modes. "Always" means that if Do not Disturb is enabled your phone will not ring, even if you are actively using it at the time. "While phone is locked" means that if you are using the phone Do not Disturb is temporarily disabled, until you lock the screen with the button at the top of the phone.

Could be a bad SIM. Or your "discconect" message did not get to the network. It is probably not an issue with the phone, but to be safe go to Settings/General/Reset - Reset network settings. You will not lose any data, but you will have to re-enter any WiFi passcodes that are stored on the phone.

That sounds like a network problem with your carrier.