FIG. 1 is a front view of a cord end stopper of the claimed design. FIG. 2 is a right side view of the cord end stopper of FIG. 1. FIG. 3 is a plan view of the cord end stopper of FIG. 1. FIG. 4 is a bottom view of the cord end stopper of FIG. 1; and, FIG. 5 is a perspective view of the cord end stopper of FIG. 1.