negative balance

hello, the charge to the debit card was rejected for not having funds and now there is a negative balance, if I pay this balance is zero? or the balance is in my favor, because I have blocked the use of the SIM card, plus an incredible charge for not having funds, from the bank and from o2, I have to pay it directly to o2? or putting money in my bank account, it's really confusing how o2 handle things.