Is a person entitled to retract his consent to not take the amount, and must I give him the amount, or is he not entitled to that?

If a person has a right over you, such as a debt, then it is obligatory to repay it in full if you are able. If he demands a right that you do not believe he is entitled to, then it is permissible to settle for a portion of it. If the denier believes the claim is false and the claimant believes it is true, then the settlement is outwardly valid. However, if one of the parties knows that he is lying, then the settlement is inwardly invalid, and what is taken through it is unlawful.

If the right-holder foregoes a portion of his right willingly, then there is no blame upon you, and he cannot retract it. However, if he foregoes his right unwillingly, then it is not permissible for you to take it, for the Prophet, peace and blessings be upon him, said: "The wealth of a Muslim is not lawful except with his willing consent."