Once a payment enters a pending/processing status, neither brightwheel nor you, the provider, can cancel the payment. This applies to both online and direct bank transfer (PADs, ACH) payment types.
This is due to processing times being managed solely by brightwheel's payment processor and the payer's financial institution.
The best way to resolve this is to wait until the payment has been completed successfully and is marked as paid. Typically, payments take 5-7 business days to fully process depending on the payer's financial institution. Then you can either issue a refund to the parent or apply the overpayment towards the student's next tuition payment.