Review on Flygo Men'S Fleece Pants Winter Warm Joggers Pants Active Sherpa Lined Sweatpants by Junior Samson

Warm pants, wearable as is in 40F degrees.First time I used it, few threads in the elastic waste started breaking as I stretched to put on.After 3 washes and at least 3 weeks of use the strings are showing wear and tear. There are signs of fraying where I tie the knot when I tighten my pants.Anyone know if I can replace the string? Or is it sewn into the pants?