I have explained why in another post. If you want it a 12 month SIM OTC, you'll have to do so via an independent. Alternatively, apply a monthly pack by yourself by tapping in the relevant code or getting a True shop employee to tap in the code for you. ☺️
If it's a 'back up' SIM, then you might want it on another network.
DTAC also has unlimited in the form of 6 Mbps, 15 Mbps and 30 Mbps.
Their 6 Mbps product includes unlimited calls to any domestic network.
The others have the same call offer as the Truemove H SIMs.
1200, 1400 and 1700 baht respectively