Xbox one achievements not showing up and gamer score incorrect

Hi my gamerscore particularly my xbox one achievements are either not showing up as completed and/ or some are incorrect. I am missing well over 100K in gamerscore. I have tried switching user logging in and out but to no avail. Some games i have completed
to 1000K appear as if i hadnt even played themcoming up 0/1000. Please let me know how to fix this as achievements are a big part of the fun in gaming besides the games themselves.

:)