The problem is that medium sized drones (professional quadcopters and Shaheds) aren't easily damaged by flak. At least not damaged enough to knock them out of the sky.
Yes, there's always the golden BB to the control circuit boards, but general damage to props or wing surfaces is basically not going to stop one. You need a hit solid enough to break the airframe. Break the main wing spar, blow the rudders off, break the rotor support arms.
By jamming the cellphone network, which also announces an attack. And the jammer is actively emitting for your artillery to smash.