You have plenty of ways to find out: 

❶⠀Directfrom BT Pay: after registering your STAR card in the app, just click on "Show balance " ;

❷⠀By application BT Visual Help: call the number 0264 308 000, menu "Accounts and transactions";

❸⠀By application BT24 Mobile Banking: from the "Finance" section , find it at the bottom of the screen, choose the "Cards" option and select your STAR card;

❹⠀By platform BT24 Internet Banking: from the top menu bar, select the "Cards" option and choose "View card";

❺⠀Direct from merchant at time of payment: in STAR partner storespartner stores, you can ask the salesperson to check how many points you have on your card;

❻⠀Prin the bank statement received by email;