What is the ruling on one who swore an oath upon the Qur’an to abandon a sin but was unable to do so, then swore an oath upon the Qur’an again not to return to the sin, and that if he did return, he would fast two consecutive months and that Allah would never forgive him?

You must repent from watching forbidden movies. Swearing on the Qur'an is not from the Sunnah, but the oath is binding, and retracting it requires an expiation for an oath for each instance. If the breaking of the oath recurs before expiation, the expiations may overlap, and one might suffice. As for swearing to fast for two months if you return to watching movies, this is a "yamin al-lajaj" (oath of insistence), and its maker has the choice between fulfilling what he swore upon or performing an expiation for an oath. The forgiveness of sins is in the hand of Allah, and sincere repentance is accepted, in accordance with His saying, "And it is He who accepts repentance from His servants and pardons sins and knows what you do."