Blizzard really need to rethink about SR penalty from disconnection. My internet just down for a bit in the start of the game and suddenly disconected, then VOILA, -50 SR for a thing i didnt even do.
Unfortunately all disconnections and game crashes counts as leaving the match and will be penalized appropriately. The game server has no way to discern a legitimate disconnection or game crash from one that is forcefully caused by a dishonest player to bypass leaver penalties. You can learn about this policy here:
It sounds like you identified that your own internet connection went down entirely, so I will just say try to make sure your internet remains stable before attempting to play competitive again. However, if you are disconnecting from the game server frequently without losing your internet conneciton, there is great troubleshooting to start with that can most likely resolve most issues and I encourage you to check them out here: