Spoke to a cso just now she told me you cannot extend the expiry via topping up the sim but by doing some actions on the sim like making a phone call or sending an sms she didn't specify if the call has to connect. I am overseas so i am not about to make a roaming call or sms so i just need to double check here with you guys if this is truly the case to extend your true move sim.

I am fairly certain that any top-up, completed out-bound call or originated SMS can/will extend the validity of a SIM.

But this is really dependent on the specific terms and conditions of your promotion/plan/SIM, and there are dozens of variations.

Can you share any details on your SIM? TrueMove or TrueMove H? What did the packaging say re: the T's and C's? What is your ultimate goal here? What is your situation? What is your budget? Sharing as much detail as possible may yield more/better ideas and recommendations.

If your goal is simply to maintain the number, and/or preserve your current balance, then maybe ask someone in Thailand to pop round the shop and add 10 baht to your number.