Dentist thinks we're done, teeth aren't corrected

I have been a perfectly compliant adult patient for ~ 18 months, investing in this orthodontic project to correct some forward drift of lower teeth that were hitting upper teeth. A lot of progress has been made, but now my front teeth have gaps in them that they did not have before. My invisalign provider expresses that we are done. I am arguing with him that I am not happy with these gaps. He says he cannot see them. This is ridiculous. After this being my 2nd time with braces in my life, this last round costing $6000, I should not look like a person that "could have a great smile if I'd just had braces in my life." I am preparing a letter in writing to mail to him, to allow him to prepare a solution BEFORE our next visit. Our last appointment resulted in nothing but a rushed argument between us and me me walking out of the door with these "retainers" that are supposed to be the final step. Any tips? I warn everyone out there to NOT pay the provider the final amount you owe them until you are completely done. I made this mistake and sense a definite change in the tone of the "customer service" from these folks, since I wrote the final check. I sense they just want to be done with me. I can promise you one thing. If I have to go to a 3rd orthodontist to resilve this issue, I will be suing the one who I just paid $6000 to, for new gaps in my teeth.