Smashed roof box from falling item

Whilst travelling on the m4 before entering the Severn bridge from England side travelling into wales an item fell / thrown from the overhead bridge causing destruction of my car roof box causing broken plastic across the outside lane. The roof box was unsafe to leave on the car incase further parts fell off into the motorway, roof box removed and left safely at the side of the road. The incident happened approximately 09.30 unfortunately due to lack of signal this is the first opportunity to advise of this