dash meter showing AT signal and car goes lamb

for recently few days i am facing a big problem which is AT signal !

my car suddenly shows AT signal when slowing down or coming to a stop and car make a high jerking and speed done both ahead and reverse


here mechanics are not very expert about Mazda . they are telling me to change the Transmission Box directly

but i can feel that no need to change transmission box cause i can easily hit 160 ~180 kmph speed

and the At signal not showing in running high speed