iPhone does not receive any push notifications

Hi,

It's probably easier to describe what my iPhone 6 (current iOS) still does: phone calls, SMS, internet surfing with Safari. However

• I am not able to connect to iCloud or iMessage,
• do not receive any push notifications,
• cannot read any emails,
• the phone does not connect to my Apple Watch,
• I am also not able to connect to, e.g., WhatsApp,
• I cannot install any app updates - the circle fills, but at the end it tells me that the app cannot be downloaded.

Instead, the iPhone keeps asking for my iCloud password, my Apple ID password and my other email account passwords again and again. Furthermore, the phone is most of the time really slow in reacting to touches (especially after startup).

Has anyone experienced that behavior before and would have some hint how to solve this?

Best regards,

Matthias