What is the ruling on disposing of a sum of money paid by a participant to a financial association, who then stopped paying and refused to reclaim the amount after an attempt to return it to him? Is it permissible to give it as charity?

If the claimant refuses to take his right, intending to hold you accountable for it in the Hereafter, you must deliver the amount to him by any possible means. You are not permitted to give it as charity unless you are unable to deliver it to him. If you have wronged him by delaying his right, you must seek his forgiveness. If you are unable to do so, it is hoped that Allah will bear his right on your behalf if your repentance to Him is sincere. However, if he waives the amount for you and is content with that, you are permitted to dispose of it by taking ownership of it or by giving it as charity.