Instead of going straight to the tax folks, I'd first have the lawyer and bookkeeper take a look at it. They'll likely know the best way to respond, citing "chapter and verse" of the code to cover your butt. Good luck.
I went there without consulting anyone first. I was also out of time. I hadn't been at home for a few days and when I got the letter the official deadline had already passed (although I'm pretty sure that the letter arrived only one or two days before the deadline). Anyway, got there and pulled a number. From a distance I could see that at my particular booth there was a comparably young woman. I thought I got lucky this time, she could just be young enough to still have a soul. My number came up, I went there, I got the coldest look ever and she used several euphemisms for "idiot" because I showed up at the wrong booth. She really went through great lengths so make me feel like shit. After two additional attempts I got a number for the right booth, from a distance I could see an insanely evil looking old hag. I felt like shooting myself at that point. Then my number came up and something magical happened: that old hag turned out to be a lovable granny! She didn't smile for the first couple of minutes but she was still lovely! She solved all my problems, explained everything and even gave me friendly advice for the future! She even fixed an unrelated issue I wasn't aware of before showing up! And in the end we both even laughed!
And that, little children, is the story of how I left the tax office with a huge smile on my face. The end.