It's usually not just 1 hacker on the game. It's 100's. There are walls built into the system to catch a majority already and there are still 100's that pass through these checks and make it into the game. You "say" you report them, but do YOU actually report them? Or is it people all recognize and assume SOMEONE reported them? Because most cases, the team doesn't know to look. The SM team is small. They all have jobs outside of banning cheaters. Sometimes it's simply lag time from ciphering through the 100's of emails they get. They have deadlines outside of banning hackers as well. 24 hours may be their deadline, but for you, you feel you've lost to the same hacker 15 times now.
Now honestly, I do not know the circumstances for the particular case you mentioned. But am simply putting it out there. There are often common assumptions made. But there is no dedicated person to banning hackers, cheaters, etc on the SM team. That's a side part of their main job duties.
Also, do note, sometimes accusations are baseless. Not saying that you should be the one investigating. You shouldn't. But if you don't submit and assume others did, if no one submitted, you can't blame staff for not looking. They aren't in game playing as you are. They don't see these cheaters cheating. They have systems already in place to stop these things, so these people have already found a way AROUND being caught by these systems.