I'm Lvl 40 on two accounts, I farm EXP in BPHills Hell 1, with 6* Lich King (+12 runes 1x DMG) & 6* Medusa (12+ runes 2x DMG). For DEF, I run 2x-4x and I've found my app tends to crash more often if I use 5+ DEF or higher for some odd reason. For ATK, I never go higher than 2x DMG. I make sure I always run the highest hero with the best runes for anything that isn't EXP farming except for my farmer as that is the key. Your heroes have to be at the appropriate level with runes for any high Lvl dungeons like Catacombs, Liar, Spire, etc or its a dead giveaway. Basically, make sure your heroes look the part when doing anything.
Since you've gotten banned, if you decide to play the game again, I highly recommend you re-roll until you can get a very good Nat5: either Medusa, Lich King, Spider Queen, or Monkey King as they will be your farmer. There might be a few others I'm leaving out but those were the ones I was aiming at.
GL, play smart and stay safe