One time, I sold a bunch of stock options because my company was being spun off into an independent entity. "Use it or lose it" kind of situation. As part of

One time, I sold a bunch of stock options because my company was being spun off into an independent entity. "Use it or lose it" kind of situation. As part of the spin-off the company was also renamed. So it created a slightly weird situation, which caused a lot of trouble for me and my colleagues. That trouble was a bill for $12k (which at the time, I absolutely could not afford). Basically, the mix-up was the IRS thinking I had sold RSU's and not options, so they had 0 cost basis and they thought I owed them the money. I contacted my former company's HR department, and they said lots of people had the same issue, and they shared the message I should send to the IRS in response. So I printed out my correspondence with the former company explaining the issue, along with all the documents showing the cost basis, with a cover page explaining the tl;dr of the situation. The IRS sent me a couple months later the same bill for 12k with late fees - now totaling 13k. So I printed out again the entire package I had sent them before, including a new cover page (on top of the old one) saying, "Find enclosed the documentation I sent you before which explains clearly I do not owe you money". At this point it was 15 pages of materials. A few months later, I got a letter back which said in legalese something along the lines of not admitting to any error, but also at the same time saying I didn't owe the money. Weird, but I took it as a win.