Budget Units is linked to Duration

Try to Use Duration type Fixed Duration and Units

Haresh,
The reason why your duration change when budget units is change because you use a duration type "Fixed Units" or "Fixed Unit/Time" and resource "Drive Activity Date" is tick. If you used this duration type settings and don’t want to affect your duration when changing Budget Units then you have to un-tick "Drive Activity Date" under resource assignment on each resource. Alternatively use Fixed Duration and Unit" or "Fixed Duration and Unit/Time". Using this settings will ignore "Drive Activity Date" settings on resource which I already explain to your before when you are querying about P3.x Driving resource equivalent to P6.