Here is what happened. You agreed on 500k a day and 2M if the account gets banned (was no limit) and you owe him 10m overall. Nobody ever accepted a "I'm done with the account deal". You then proceeded to pay 100k for that day and 3 days later the account was banned. Lets face it, it's quite difficult to have a secure account once someone gives it away (he gave it to you) so you are basically it's owner, especially because you didn't pay him the 500k. I cannot say who got the ban, but the account should have been under your possession, and regardless of your responsibility for the ban, you still owe him the full 500k. I added the 2m because that's what you agreed on if the account got banned.
Now, you said you weren't paying him anything, and that means you wouldn't refund the 500k you'd have to pay regardless of the timeframe in which the account got banned.
You've been banned and if you wish to come back you may refund the 500k and post an appeal