To check account balance use *121# and finish with the dial button.
⏩ How to find out my number in AIS?
To know your phone number use *545# and finish with the dial button.
⏩ How long can I keep my number for if I don't use any of AIS services?
If the SIM has 0 balance and is not used for 60 days, it will expire. However, you may also keep your number for up to 30 days without using service. Just dial *500*9# from your AIS. Note: Keep in mind that there will be a fixed fee which will be deducted from your balance.