Did you claim a deduction for the fee on your 2015 tax return - perhaps by including it in your itemized deduction for mortgage interest on Schedule A? If you didn't deduct it in the year that you paid it, you don't have to report the refund.
How did they pay the refund? Did they send you a check, credit it to your 2018 mortgage payments, or something else?
Did they send you any kind of 1099-series form showing the refund? If so, what form, and which box of the form is the refund in?
