There are several variants in this situation:
1. You sent funds to an email address which turned out to be registered on the trading platform.
3. You transferred money to the wallet address.
In this case the transaction can not be canceled. You should contact the owner of the wallet and ask for a refund. If you do not know the owner of the address, then unfortunately you can not return the funds sent by mistake.
We strongly recommend you to be careful and attentive when sending funds. Before transaction make sure that the address you send money to, exactly matches the address of the recipient.