Hello @Taco-man2022 , welcome to Discussions!
I am sorry to hear you received the Temporary ban in game. Unfortunately, the temporary bans can not be lifted.
MMR rollback occurs when players you've encountered in Ranked matches are identified as cheaters—in this case, they were DDoS-ing. Your MMR gets readjusted accordingly to cancel out the cheaters' effect on the affected games.
For more info, check out our Dev Blog: (http://rainbow6.com/mmrrollback).
Please let me know if you have any other questions.