I could only send pictures on whatsapp or similar apps through wifi, bu
t wouldn't be able to send picture / voice message through mobile data.
Welcome to the community!
Are you trying to send the pictures using mobile data from within Whatsapp or similar apps or are you trying to send the pictures via text message or MMS?
Are able to use data at all? If you're not able to use any data, have you verified that your phone has data enabled? You should also note that data needs to be enabled in order to send/receive MMS even if you're connected to Wifi.
What phone are you using? Have you verified that it is using the correct APN? You can verify the correct settings here.
Hope this helps