Company switch at pickup
A company switch at pickup means the truck at the curb is not the carrier you were given. The substitution clause either allowed that change or it did not. Get the new MC number and look it up before the keys move.
You expected one carrier. Another truck is in the street. Sometimes the broker assigned a substitute and told you. Sometimes the first carrier refused the rate and a stranger showed up asking for more money. Those are different events, and the contract is how you tell them apart.
What the clause has to have done
If substitution is allowed, you should have received the new legal name and docket before the driver arrived, with time to look them up. Authority has to be active. The price should be the price you agreed, unless a re-quote was accepted in writing. If substitution is not allowed, you can refuse the pickup.
What not to do
Do not release the car to be helpful, and do not pay a new cash amount to keep the schedule. Call the company on the order confirmation. RideShipper did not send the truck and cannot swap it back.