Check engine llight stays on the mechanics can't find anything wrong this started when i fill up my gas tank each time it is worse with stalling effects

If the check engine light is on, there has to be a trouble code in the on board computer. If the light only comes on when you fill your tank, then the problem is intermittent and the mechanic would need to scan the computer while the light is on. This could be the reason they can't find anything wrong. If the light is on when they scan the computer, they must have recovered a trouble code. If there is no trouble code to be found, then the mechanics will need to fall back on their ability to diagnose a problem without the use of electronic crutches. If they cannot, or will not, put forth the effort to solve your problem without the help of the computer codes, then I would suggest you seek the advice of a "real" mechanic. The problem seems to be fuel related, so the first place I would look is the fuel pump with it's integrated fuel filter. Not a cheap repair, especially if it is not the root cause of the problem. You did not say what, if any, tests the mechanics have done. They need to check for sufficient fuel pressure at the injectors. If the fuel pressure is not up to the recommended levels, then go ahead and have the fuel pump and filter assembly replaced.