Hi @R Artes
Welcome to the customers help customers Community of Vodafone.
First, I can tell you that if you use 4G over WiFi, you don't have to do anything with your modem. No ports to forward, really nothing at all.
I think it is best to delete your network settings first, then you will lose all router settings on your device, but that is what we are going for!
Then you turn your device off completely and wait a minute and also briefly turn your modem off and on and then turn your device back on.
Make contact with your router / modem again with your device and then I actually expect that it will work again. And of course also turn on the 4G over WiFi function.