How can one respond to those who deny the concept of abrogation (nasikh and mansukh) in the the Qur'an and err in understanding it?

The discourse on abrogation (naskh) has been presented in previous fatwas, and those fatwas clarify the truth regarding the issue of abrogation, and the invalidity of the statement of anyone who denies it or affirms it and claims that it can occur after the death of the Prophet, peace be upon him, through an Imam or otherwise. This is invalid due to Allah's saying: "This day I have perfected for you your religion and completed My favor upon you and have approved for you Islam as religion" and His saying: "O Messenger, announce that which has been sent down to you from your Lord; and if you do not, then you have not conveyed His message. And Allah will protect you from the people." And we are certain that the Messenger, peace be upon him, fulfilled the trust, conveyed the message, and advised the Ummah, leaving it upon a clear path.