If you have returned an order in its entirety and the full amount of the order is refunded, any upcoming payments will be cancelled and any payments you have already made will be refunded back to the card you paid with.
Afterpay refunds are deducted from any outstanding orders within your account. If you have not received the full amount back, it will most likely have been deducted of an outstanding order.
If you have any further questions please refer here or reach out to Afterpay customer care:
https://help.afterpay.com/hc/en-au/articles/360031623571-How-do-Refunds-and-Returns-work-at-Afterpay--