Same problem for me about ban time, but i always use new accounts with Aimbot (before wasn't play with Aimbot ) also cannot change my real ip i think because of that the ban comes after short time. What about you can you change your real ip?
Anyways i tried playing without Hack they also banned me for nothing really but K/D was 4 .. After that i decided to play with hack again.
For me i think my ip is flagged as a cheater thats why when reach level 24-25 account get ban so i will try to reach level 20 then leave the account and create new one and will see the results .. I checked the account they banned without hack they ban me when reached level 25 almost 3 accounts same problem..