Conflicting confessions of a litigant

There are witnesses who paid on Sunday and there are witnesses who paid. The borrower claims that I did not pay (a party’s statement that he did not pay). The plaintiff claims that I only paid on Wednesday (a party’s admission that he did not pay on Sunday). What is the law? Alexander’s method of scrupulously observing the heads is not appropriate here because each person is suing his neighbor with force.