Returning to IAH from car rental center. Any free shuttle?

We're returning our rental car at the rental center and need transport back to IAH afterwards.

They gave us a free shuttle from the airport but want to charge $35 to go from the rental center back to the airport.

Is there actually a free shuttle and the $35 is for a different service or is there actually no free shuttle back to the airport?

We're on an international flight if that makes a difference.