Winky, submit your written request in person to the bank asking for "STOP PAYMENT OF THE CHEQUE#XXXXX". Give all the details about that cheque like Beneficiary name, amount,date written on it. They might ask you to give details why ur marking it STOP PAYMENT.
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They will charge you for your instruction and will mark it STOP PAYMENT in their banking system
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BE AS QUICK AS POSSIBLE. Don't wait a minute