Forwarded call message

[Akhil TC]

I got a call from my dad's number and I get a message along with the call saying "Forwarded call(Call forwarded unconditionally)". This happens even when he calls to one smartphones of ours. We thought that the problem was in the phone and we changed the Sim to 4 smartphones and tested. It still shows the same message. Does that mean someone is spying on that number ???