"Early in our relationship things were fine."
- 11 Years ago things were different.
I would bet that the quality of this "relationship" is in line with your Debit Card usage. In that the more you used your Debit Card the less fine the relationship became. Previously you probably either wrote checks or used cash. With cash you went to the ATM once and pulled out out a set amount of money instead of swiping your Debit Card 5-6 times for various small transactions. This act alone decreases the amount of your overdraft fees(if you do overdraft) significantly. In writing a check you could "hope" that the check will take a couple of days to get to the bank in effect "floating" the funds. So you never noticed how they post your debits or credits. But you can be pretty sure that it has been debits then credits for a very long time. It just didn't matter because the "debit"(check) came in after the credit(deposit).
If you do not have the money AVAILABLE in your account when you swipe your Debit Card or even write a check you have the very real possibility of over drafting. Yes, making sure you don't spend more than is available is a way to make sure you do not overdraft. Because then no matter how they post the transactions you won't go negative. If you don't go negative they can not hit you with Unavailable Funds or Overdraft fees.
"I am filing a lawsuit against them because not only have they sent me into financial distress but they are also unwilling to fix the error"
- Again the "error" was on your part. But what legal grounds are you filing the suit. Keep in mind that everything is disclosed to you when you open the account.
"am not looking for damages or restitution just what is owed me."
- I suggest you look up the term restitution.
If you really do keep track of your money and this is just a case that you don't know how the bank posts the transactions, take it as a learning experience(yes an expensive one). Because if you go to other banks, there is a very good chance that they post debits before credits. So be sure you know and understand how they do this before you open up your account.