To answer your question: No, that is not true.

Yes, the old products are being discontinued. AIA's rebranding exercise after acquiring ING began in 2013. A completely new line of products were launched and the old ones being discontinued (but if you hold the old policy, it is still in force and you still enjoy all the benefits spelled out in your policy contract. You just can't buy old products anymore).

If your existing plan is an investment-linked plan (beginning with the letter "U" followed by numbers, you can just upgrade on your existing plan. There is even a special calculator to generate the difference in premium for your medical upgrade, or even to add in new riders.

Now that all technical stuff is said, is the agent memang your existing agent or is she an agent that you're dealing with for the first time?
If is an old-timer...quite bad la.
But if is a new agent that you've never dealt with before, by upgrading your old plan she won't get any commissions at all.

Another thing you can do to check on your options available is to go to any AIA branch office. Our CS are more than capable to help you out. 

Bro, understood now and u guys are true professional. The existing agent resigned and reassigned to the district manager which already upgraded me with the medical plan. As for the other agent which is ex-ing...right to say that upgrading will not bring her commission and thats why propose new package.
Perhaps i should stop engaging her for my other plan....

You'll have to answer a health questionnaire (truthfully la  ) and it will be submitted to go through a normal medical underwriting.
In that process, your old plan will still be active.
(If I do remember correctly, I think there is a campaign going on in AIA for existing AIA customers, where the company is offering a prorated refund of last premium paid if you upgrade to the new plan. Please privately follow up with me on this.)

In the case where your medical upgrade application is approved, your medical plan will still follow your old plan for the duration of 4 months (all the waiting period). After the 4 months, it will then be fully transferred to the upgraded plan.

Should there be any pre-existing conditions (meaning anything before the time of applying for the upgrade), it will depend on the underwriter's decision. Normally if you have the medical reports, we submit together is better la.