Orthodontist drilled gaps in bottom teeth for Invisalign. Now treatment is over and gaps haven't closed - advice?

My orthodontist drilled gaps in my bottom teeth so that my teeth could shift accordingly to Invisalign treatment. But now all of my aligners are finished, and the gaps are still there. He tried to dismiss the gaps when I addressed my concern by saying it is hardly noticeable. I went back because I couldn't stand the chunks of food that would get caught in the spaces and now he's charging me for 5 additional aligners for 1400$. Is this standard? I have Invisalign lite. What can I say or do?