When you add a payment method or at time of booking, we may place a temporary authorization that will eventually be voided, and not charged.
The time to void depends on your bank's policy. Occasionally you may also find recent charges for past trips that have been delayed in posting to your bank. To check you can tap History or your Grab receipts to verify past trip amounts.
Let us know, after verifying not a temporary authorization or in fact a charge for a past trip, if you still believe there is an unrecognized charge.