Make sure you save all those letters, lest you resolve the error and get a letter several years later saying you owe $x + interest due to an error that you’ve already resolved. Because they don’t have those records digitally, apparently, and if you don’t have paper copies of every document involved you might just get to pay that penalty whether it was ever due in the first place, or even if you’ve already paid the penalty. Or get a lawyer.
Which is what happened to me the year before last.