BNP bad Conduct - Help (Legal Advice) (Brussels)

I have a problem with BNP Paribas, and I am not sure how to proceed anyone could help me please? Here goes the problem:

I’ve requested and overdraft agreement one year ago, I’ve been told and confirm by the bank that the agreement had been approved. I’ve never used it.
I also have a credit card. Last month I’ve used the credit card, At the end of the month the full amount has been deducted from my current account to pay the visa card, so my current account went on overdraft. I’ve received a call from branch that I need to pay before the end of the month if not I will have legal problems with the bank. When I mention my overdraft agreement, they told me that I don’t have that agreement and I need to pay. When I asked why I don’t have it, I haven’t received an answer, and a quote "you need to pay and after we will see".
Anyone know what could happen if I dont pay? I do have the money but the bank cant cancell an agreement without warning/ notice.
I ve tryed to talk to them, nothing, I ve called consumer rights, nothing. Send e mails to legal department head office nothing... What could I do??!!

Thank in advance for your help!!