Coingate: In case of overpayment of your order, we do not receive the amount of the overpayment, so you need to follow the link yourself and create a request for a refund of your overpaid funds: https://support.coingate.com/hc/en-us/requests/new.
MixPay: with this payment provider the situation is the same as with Coingate. Please use this link to request a refund: https://help.mixpay.me/en/articles/6836092-how-to-contact-customer-service. Or just write to: customer@mixpay.me.
NOWPayments: please contact our support team creating a support ticket so we can help you.
If you have overpaid for an order using another payment provider, please contact our customer support team by creating a support ticket.