Child Seat Positioning Clip problems of the 1996 Dodge Grand Caravan

My daughter who is 23mos, 35inches, 31lbs, is able to remove the toddler chest clip and push her arms out of the shoulder straps. Century has a locking clip but fisher-price does not. F-p has offered to take the seat back for a full refund since it is no longer safe for my child, and they do not have a solution to the problem. I worry about other children being able to do this. Up until now I was quite satisfied with the design of the seat.