I hope that your return was not cross-border*.
If it was I hope that you marked the parcel as 'returned merchandise'.
UPS is notoriously expensive for cross-border shipping, due to their high ($25+) customs brokerage charges.
"Returned merchandise" is not charged duty.
An unexpected need to pay and then be reimbursed for unnecessary import fees is not a good way to make a transaction go smoothly.
You may already have learned this if your seller used UPS to ship to you.
And of course, you can get the duty and sales tax you paid returned by calling CBSA. The number should be on the back of your UPS receipt.
*These problems do not arise if both buyer and seller are in the same country.