there are a few threads/posts about this - you cannot go over 2 bil with either the bank or inventory or it will go to 0..with bank it will go to negative penya.
im not a GM but since theres warnings all over the place im pretty sure you will not be reimbursed anything. in order to hold more money, make more characters in your account and have 2 bil on each character and in bank...12 bil per account