Yes this happened me on our trip that ended yesterday and I was sooo upset! The first time was for Cinderella lunch that I changed to a better time that was outside the 2hours but on the same morning as the adr, I was worried I would be charged full price for both times, but I called the Disney dining number they said to call and I was able to cancel.
2nd time was beaches and cream but for the next day. This time I went to the front desk of AKL where I was staying and they canceled it for me. I wished I would have went to the front desk for CRT too instead of panicking and having to wait until the dining line opened.
Very annoying but go to the front desk if you can. My call to Disney dining took 15mins calling right at 7 until someone picked up. I’m not should what else to do, unless you can go to the restaurant directly and ask them to drop the time you don’t want.