Started stuttering and then switches off

A while back, my atos 1.1 started stuttering and then switches off. After switching off and on it could be driven again but then it struggled. Was told the gearbox had packed up. Had the gearbox changed last week. However after 50km on the road, it did exactly the same thing. Stutters and then switches off. No acceleration power. It took 20 minutes to drive the car 3 km without any traffic due to loss of power. Please help, have now spent more than the book value of the car