Is the agent's verbal notification that the client does not want the extra materials sufficient, or is the client's signature required for that, or is a phone call from the agent to the client sufficient?

If the remaining materials are negligible and the client has abandoned them willingly, it is permissible to take and utilize them without the client's permission. In this case, they are considered like abandoned crops or dates that become the property of whoever takes them. However, if the materials have significant customary value, it is not permissible to take them without the owner's permission. It suffices for a trustworthy representative to convey the client's permission. If the company wishes to take these materials in exchange for its work, there is no objection if this is done by agreement and mutual consent with the client; otherwise, it is not permissible.