The first 6 digits of your credit card number form the issuer identifier
VISA Starts with 4XXX... total digits are either 13 or 16
MASTER CARD With 51XXX to 55XXX... and total digits are 16
American Express is I think.... 34XXX and 37XXX and total digits are 15
Only the owner of the card can verify the remaining balance on credit card by calling the number given on the back of card..