That sounds incredibly frustrating. Could you try reaching out to both the neuropsychologist and the assistant one more time and say something like, "If I don't get a response, my only option will be to file a board complaint. And I''d prefer not to have to do that." Then you're showing you're serious and giving them one last chance to comply with what you need. If you don't hear back in a reasonable amount of time (I wouldn't count this upcoming week, as many would be on vacation), then go ahead and file it. Or perhaps contact the board and ask if they have any suggestions.

It would be completely reasonable to just submit a complaint now, though, if you don't want to or can't wait (like if you'd need to file with your insurance by a certain time to get reimbursement for services from this year). Though a complaint might take a long time, so trying one more contact first could potentially be faster, if they actually respond.