Need some advise cause my health insurance won't uphold their 75% coverage

Hi guys,

So I went in today to get my deep cleaning done. The procedure 2 quadrants of cleaning which is my lower jaw and splinting my front tooth. However upon paying, I was told that they would only cover 1 quadrant of deep cleaning (item 222 - root planning) and the splinting. So I have to fork out the entire 2nd quadrant which is 450 by myself. I called up by insurance, GMHBA, and they explained that under their policy they only cover 1 quadrant per day which is 6 teeth.

I find it ridiculous as no way in my care package was this mentioned and I have called them before and they have not mentioned that to me either. When I made this argument, they said that yes the information was not on their care package due to the fact that dental claim can have a long list of items and would be too much to print out. Also there are more than 6 teeth in a quadrant. I tried to speak with their supervisor and was put on hold for some time before I was hung up on!

I'm just wondering what can I do at this point to not have to pay the extra cost I forked over? If I had known about this then I wouldn't have gotten it done all at once today. I know for a fact that I would case them up tomorrow again regarding this issue. Any advice would be much appreciated!