If you want to cancel a voucher, you can do it directly from the admin in the voucher tab.
Please note if you cancel a voucher from the voucher section, the customer will automatically be credited back to his wallet account.
Two scenarios then exist:
Purchase vouchers generated on new or in store
You want to re-credit the customer with the amount of his voucher: you will have to remove it from your checkout system
If you do not want to credit the customer again, his credit will have to be deducted from his wallet.
Second-hand site-generated vouchers
You want to re-credit the customer with the amount of his voucher: the BA will be automatically deleted and the customer will be credited again
If you do not want to re-credit the customer, his credit will have to be deducted from his wallet