This is not the first time it happened. But I will usually top up my card at least $20 and then it will just kept deducting my main balance for no reason and leave my "free bonus credit" untouched.
This trip after I purchase my $10 / 1.2gb / 30 days, I still have about $19++. After 2 days in Bali, my main balance dropped to $5++. And I only realised that when I got into an accident and urgently need data to get help but my data lost connection because of the minimum $8 limit.
How can I apply to see how the main balance is deducted as a whole?