If anything is given to a creditor by way of performance that the creditor refuses to accept as performance, the creditor is not bound to return it without demand but, if the creditor retains it, the creditor is a gratuitous depositary of the thing.
Creditor's Retention Of Thing That Creditor Refuses To Accept
Mont. Code Ann. § 28-1-1113, under Extinction of Obligation by Performance.
Mont. Code Ann. § 28-1-1113