I have purchased the EGO 15-Inch Pre-Wound Spool with Line for EGO 15-Inch String Trimmer Models ST1501-S/ST1500-S. After following the instructions on the package, cross-checking with the manual. When I press the lock/trigger, the line starts continuously feeding until I release the lock/trigger. I managed to destroy one spool, then bought another with a similar result, although I salvaged the line. I had a neighbor, who maintains lawn equipment try to reload it following the instructions, and he experienced a similar result. Need some expert assistance, please. Thanks!