Pokemon go doesn't work when I'm connected to wifi. It still says that there is no internet connectivity. Is there any way to fix this? I have an old phone(karbon sparkle v), perhaps there is something I need to change or set up in settings? Or is it just a game problem? How can I fix it?
You need to distinguish between WiFi connections and Internet connections. A WiFi connection is just that - a connection to a WiFi access point which is usually a small box with 2 or 3 little antennas on it.
It is usually connected to a local area network (LAN) which has a connection to the Internet itself. If the LAN is not connected to the internet, your WiFi connection won't be useful for anything but connecting to other computers or printers on that same LAN.
You will need to determine who owns the WiFi access point and ask them if it can be connected to the internet, or find another WiFi network that is connected.
Is that works with your Mobile data? If it works with mobile data and not on your wifi, try resetting the phone.
If you are unable to play the game in any mode, try calling your network provider. Before that check the Pokemon go server status as well. You can check the server down status by checking here and here.