I recently read about a man who failed to review his credit card statement, didn't notice $11,000 in fraudulent charges, and is currently on the hook for them because he's technically paid them off. (Via Bargaineering.)
There's a huge lesson here for all of us: Always check your monthly statements, because it'll be difficult, if not impossible, to get your money back once you've paid the bill.
I do this with credit card bills, and thanks to online account access, I actually check the charges several times a week to make sure nothing is amiss. (Ditto for our bank account balances.)
I even check utility bills, medical bills, and pretty much every bill that crosses my desk to make sure the amount is about right before I pay the bill. Certain bills are about the same amount every month, which makes them easy to review. (Our landline and cell phone bills fall into this category.)
Utility bills fluctuate more because we're not on a level payment plan and rates increase over time, but the bills always have the usage numbers from the previous year. I check to see if they're similar, because it's unlikely that our usage has changed dramatically from the year before. If the numbers differed significantly, I would wonder if the meter was read incorrectly and call the provider. But until now, the numbers have always been similar, indicating that the amount due is simply higher because of a rate increase.
With medical bills, I always check them against the explanation of benefits (EOB) statement that I received from the insurance company. This has saved me a lot of money over the years. For instance, I recently received a bill that I couldn't match to an EOB, and there was no EOB for that doctor when I checked online. I called the doctor's office, and the receptionist figured out that they had entered the member ID number incorrectly. Once the insurance was processed correctly, our portion of the bill went from $100 to just over $5.
So remember this lesson: Always review your bills before you pay them. You could end up saving yourself a lot of money!