Hey there @raymchan,
You explained that your June invoice was $111.98. You also explained that you made three payments. Two payments of $59.26 and one payment of $52.72. This would indeed leave you with a credit balance of $59.26. You did the math yourself in your first post.
Keep in mind that your July, August, and possibly even your September invoices have been billed since.
To view your payment history, simply select the Payment History link on your My Account Overview page:
Also, your balance is displayed just left to the View Bill link, as shown in the above image. You can also follow my colleague @FidoFaiza's advice and dial *28 to confirm your current balance.