There are two ways as told by my SA:
1. You pay full premium for new car, then baru transfer the old NCD to new car, and get refund from the new insurance coy.
2. You top up money to withdraw your existing NCD to transfer to new car. The benefit is your new car premium should cost more than the old car so your capital outlay is lower compared to option 1.

My experience recently (I chose option 2):
1. Telephoned the insurance coy saying I wanted to withdraw NCD as I booked a new car. I called them a few days before my new car was due.
2. Insurance coy emailed me some forms to fill (NCD withdrawal, credit card payment slip) and sign, after telling me how much I need to top up for the old insurance for the remaining insured period.
3. Filled up the forms, scanned and emailed them.
4. They emailed me back with the NCD withdrawal notice, iirc on that same day or the next day.
5. I just had to show my new car SA the letter, but he did not need it as he told me his computer system had already indicated my available NCD for new car was 55%.

Your SA is lousy as this should be a common thing and he should know how to go about doing it.

+1

How did you transfer the NCD - the procedure?
Your new car policy should state the NCD, and it will be the same NCD as your old car if you did the proper transfer.

I checked mine which was transferred in August this year, -under old car plate the NCD has become zero, whereas it reflects the actual NCD when I key in my existing car plate number.

I'd call the SA and current/previous insurance companies to find out what happened.