As an Account Receivable Controller, what would be the best approach in collecting the Disputed receivables from Old customers?

Give Them Nice Deal To Encourage Them To Pay The Old Outstanding Amount, Like Give them some of Goods stagnant may be it helps them but not helping my company to achieve profit or make deal with them to installment the old outstanding amount on monthly basis for long period after that if no response we can start the law road with all supporting document.