Yes, the card should work overseas at ATMs and payment terminals (I've used it in the past many times), but you may need to adjust the limits and as with any foreign card, it sometimes fails for risk controls or seemingly random reasons.
After my account was frozen, I could still use their app, see my balance, and adjust settings, but any payments fail after the last confirmation step with a generic message to call them.
So if you just want to test whether your account is frozen, try a 20thb topup for your mobile number or a small QR payment or transfer.