There have been some changes to how transfers from my OD line of credit work and I never received any notice about the change. Previously, if I purchased something that cost $15 more than I had in my checking account, $15 would be transferred from my OD line of credit. At some point, the bank changed the minimum transfer to $100, so I would(in this case) have $85 extra in my checking account. I never received any notice stating that the bank would start doing this, and months passed before I even noticed. Isn't the bank required to inform me of the change since I'm paying interest on $85 more than I would have under the old system?

Call your bank and ask them when they made the change. I'm willing to bet that they made the disclosures and used a statement stuffer or a tag line on a statement to convey the change. They can tell you how they communicated the change and can probably give you a copy.