I have a stomach surgery scar since when I was about 10 or 9 years of age scar is open form tip hasnt healed and has puss, doctors all say leave it alone and it will heal. 11 yrs now and now and still no change what do I do

Expertise needed. You need to see a real, full time wound care doc. Infection for so long is absolutely unlikely as infections do not smolder like this. You most likely have a piece of suture at the base of the wound that has moved up close to the skin where your body identifies it as foreign body trying to get rid of it. Wound care docs are trained to look at causes of wounds and not start illogical treatments.
Infected scar. Possibility of very long standing infection of the scar. May need to culture the drainage. Systemic antibiotics, topical bactroban (mupirocin) may help.
Hard . Hard to tell without a picture, but sounds like you should see your surgeon or go see a dermatologist to discuss the diagnosis and treatment options. Perhaps a bacterial culture would be helpful since it sounds like it has pus. I hope that helps.