dealing with rude and disrespectful pre-teen?

I (23F) parent my younger brother. I'm not a parent, I'm a guardian but I hope I can get helpful insights from real parents because I am so overwhelmed that I feel like crying out of frustration every day.

He's 13 and with his generation, he has access to the internet and social media. He's so rude and disrespectful. He talks back and whenever we would talk to him about it (gently or with authority) he would cover his ears and pretend like he's not listening. I'm so tired. I try to hold our house together, my parents are old and my father is newly bedridden so I took the liberty to look after my brother to ease my mother a little but I just can't handle the disrespect and rudeness. There really is no reason for him to act this way, he gets everything that he wants and ever needs and our parents were never abusive.

The reason I posted in this subreddit because I want to have hope that this phase would pass. I don't know what to do anymore. I tried changing the wifi access because he got so rude that thats the only thing I could control but he managed to get access from our mother's phone. My mother just gave up, she believed she has done everything (and she did) and she's just letting go.. but I just can't let go of him being openly rude to us like that. I'm scared that he might grow up like that. We've tried everything, we tried talking to him and we tried taking away his gadgets, but he just didn't care. He

I know my parents are accountable for spoiling him but this is my situation now. I don't know what to do. I'm tired and so frustrated. I feel like a failure. I feel like I need to something more but I think doing something more would just aggravate him more and he would just act out more like he does.