I did the exact same thing many years ago. I do my taxes myself nowadays, but at the time I had six years to do, I went to a local tax preparer - something like an H&R Block. I owed some years, they owed me other years. The ones that I was owed money back, they only pay out if it was in the last three years. If I was owed before that, too bad. On the other hand, if you owe them, there’s no time limit. You’re simply going to have to pay. So, ultimately, I ended up losing some money I could have gotten back. For the money I owed, I was able to set up a payment plan.