A problem, however, exists in regard to the question of whether payments which have been made on the basis of the duplicate assessment have been made voluntarily. The law is well settled that where taxes are paid by one who was not under legal duress to pay the same, then such payment is considered to be voluntary and the taxes so paid cannot be refunded unless they were paid under protest (see, Mercury Machine Importing Corporation v. City of New York, 3 N.Y.2d 418, 144 N.E.2d 400, 165 N.Y.S.2d 517, and cases cited therein) . However, while payment under protest is clearly notice of involuntary payment, it is possible to show that payment was not voluntary even though it was not made under protest. Thus, where payment is made due to a material mistake of fact, namely, where it can be presumed that payment would not have been made if the facts were known at the time of the payment, such payment is not voluntary and the taxes so paid may be refunded (Adrico Realty Corp. v. City of New York, 250 N.Y. 29, 164 N.E. 732; Tripler v. Mayor et al. of New York, 125 N.Y. 617, 26 N.E. 721; Redmond v. Mayor of City of New York, 125 N.Y. 632, 26 N.E. 727; Matter of Village of Delhi, 201 N.Y. 408, 94 N.E. 874).