whats app problem on Iphone 6s

Since a week or so Whatsapp only works when I have the app open on my Iphone. When the app is closed it is not connected to wifi or 4G. So I do not receive messages, and therefore also do not receive notifications or get my whatsapp web started. I have not changed any settings and have of course tried to turn my phone off and on, flightmode on and off and all other obvious things Whatsapp support mentioned when I requested their help. I receive notifications from other apps as normal. Have IOS13.4.1 on my phone. As far as I can see my Whatsapp software is up to date. Hope somebody out there can help me. This is very frustrating.