anyone here premature ejaculation? i have this problem and dont know how to fix.

if girl start in cowgirl i usually cant last long enough to change position. after she grind a bit i tell her to stop. sometime the girl stop and few second later continue grind. i cant control and lose sperm. why she continue when i tell her to stop?? and sometime she smile or laugh. i find very embarrass. can someone give me tips?