Bank Overdraft fees on Available Balance?

My bank charged me $210 total for overdraft fees 6 at $35 each. I made an ATM deposit of $599. The receipt says posting date 3/5 by bankstatment shows a deposit on 3/5 for the $599. They are trying to tell me that my availible balance went into the negative on 3/5 as they were posting check card authorizations to my account because only $100 of the $599 posted on the 5th the rest was availible to me on 3/6 which is when the overdraft fees showed up! They are refusing to credit any of the fees back to me. They only thing they keep saying is that I went over my availible balance and not all of my deposit went in on 3/5. I have online banking and check it all the time I never saw it go over not once! Besides the money is right there! Any advice as a single mom I can't afford this ecpecially since my ex refuses to pay any child support. I filed a claim with the BBB this morning too. Thanks.