1. Part of the wall crack, already fix during 1 month warranty period ( repair several times since it occur 2 to 3 times at the same time after repair
Secondary and tertiary settlements takes time to complete. Think you got cheated if warranty only 1 month

2. Crack still occur after warranty finish and occur at same spot
It will not stop as settlement still not complete.

3. Contractor registered with cidb
does not makes a difference

4. We got into arguement since he just said the crack is surface only(block my number already)
usually any crack less than 2mm width is just cosmetic. Any wider consider structural cracks. Kinda useless if you continue arguing with him

5. Type of repair done
a. Hack a bit and plaster back
b. Hack and put cement inside
Doesnt work until settlement has completed as gap will only grow wider when there is more settlement

My questions :
1. Can i take law action to the contractor?
You can but it takes lot of time and money and usually not worth the effort. Cases can take 10 years to resolve. You need documentation ie proper agreement for works, invoice for work done etc.

2. If yes, which channel should i choose? Tribunal? Cidb board? Kpkt?
Think tribunal has a 5k limit on claims. Do you have evidence you hired him to do the job?

3. Should i hire civil engineer to assess the problem first ?
Better talk to a lawyer first. The engineer can provide documentation to prove in court. I guess your problem stem from inadequate foundation works resulting in uneven settlement which I think can be avoided if you first hire an engineer to do the construction drawing rather than when problem arise.