What is the ruling on the prayer of one who missed two prostrations and the sitting between them in the first rak'ah, and completed the prayer with the Imam?

If the Imam's voice cut off and he stood for the next rak'ah, it was obligatory for you to complete the rak'ah you missed (by sitting between the two prostrations and performing the second prostration), and then follow the Imam. Since you did not do that, it was obligatory for you to perform one rak'ah after the Imam's taslim (salutation) to make up for the incomplete rak'ah. Since you also did not do this, it is obligatory for you to repeat the prayer.