what I do is before it expires, I top-up 20Bht x 12 times via my bank app. After 12 months is reached, all other top-up will be just credited to your account, without any months getting added.
Once I forgot to do any transactions on my bank account (I forget the period) and they sent a letter saying it will be made a dormant account - I immediately deposited some money and prevented that situation.
This way, the SIM and the bank see some activity from my side and keeps them 'alive'.