If the transfer/RF payment was made more than 1 business day ago, it is not possible to cancel the payment, as it has already been forwarded to the recipient/beneficiary organization. You will need to contact them to have the amount refunded to you.
A transfer or an RF payment can be canceled on the business day it was made, or the very next day, and until 10:30 & 14:00 (depending on the time it was made).