This happened to me this year. I had a domain for almost 20 years that was on register.com. I refused to pay their fee, the discount codes no longer worked, and they made it very difficult to transfer (I made a few attempts). Eventually I got fed up and let it expire.

It was instantly snagged with a $8500 price tag to get it back. Fortunately I had moved off every meaningful account so all they were left with was a bunch of spam. As much as I liked it, it was nice to make a fresh start with a new domain.