2001 Chevy Cavalier new struts

Suspension problem
2001 Chevy Cavalier Front Wheel Drive Manual

I have just replaced the struts in the rear both sides. Upon driving the car for about 50 miles. The center of the strut had punched through the top plate that holds it in the coil spring, that holds it to the car. The center rod is touching the under side of my corner panel in the trunk. Is it a faulty strut or top peice that holds the strut in the coil spring, any advise will be welcome and greatly appreciate it. Thanks