Migrants to IJ, 2007

It's supposed to revert to "whatever you had before you got a paid account." If you had a Basic account before you went to paid, you should send an email to LJ or open a support request, to let them know that their coding isn't working.

Which they're not likely to fix, but lodging the complaint makes them consciously pay attention to it. And it might bring it to the attention of someone who didn't know that they're ignoring users' desires to not see ads.