My Employer has given me a wrong CP21 leaver form

My employer has given me a wrong CP21 leaver form. To my surprise I found that the amount mentioned in the CP21 form includes my salary allowances. When I went to the LHDN office they said my name is not registered with any of my passport numbers and so I had to open a new Tax id number after I have resigned. I was wondering what the employer was doing deducting all the taxes all these days while paying me. My Employer is Maybank Malaysia by the way, Later I found that the tax claim amount was exuberant and then I found that the employer has included all my allowances as taxable which is wrong. Now I am not sure how I should make corrections in this claim and claim back the additional amount paid to the tax office. IF anyone can give me some suggestions it will be really appreciated.