This actually happened to me, but fortunately I never actually used the domain. I registered tweed.dev intending to use robert.tweed.dev as a personal blog. It wasn't classed as a "premium" domain and the first year was £5 or something IIRC, which was half price compared to the normal renewal fee.

The next year they decided it was premium after all, and wanted to charge £492,000 for renewal. I still have a screenshot of that, although needless to say I don't own the domain anymore.