Spinosad is not very effective against mites. It is helpful in the sense that anything being sprayed on the underside on the leaves is going to kill some, but it is supposedly not chemically effective against them. I have read some anecdotal evidence that folks have had success with it, and I use it in preventative rotation myself, but never noticed it taking down any mite problem just like I never noticed neem oil taking down any thrip problems.
Neem oil this far into flower is not recommended, but you might want to try one application, followed by removing all leaves that have any sort of speckling damage. look for ANY speckling damage of any kind and remove it. This will help remove a lot of their eggs. Instead of follow up applications of Neem, order a couple thousand ladybugs, and daily, inspect for any signs of new speckling. Remove absolutely any leaves that look off every day. You should be able to keep the population knocked down enough to finish the run that way.
You can also try this instead of neem:
https://www.arbico-organics.com/product/green-cleaner-mite-control/mite-control
I have not used it, but have heard good things about using it during flower instead of Neem. In this route, spray every 3 days and remove speckled leaves daily for 21 days straight. This will effectively cycle through a few generations of mites, and you should have killed almost all of them after 3 weeks.
Goal here is to not allow the problem to run away from you. You have to be proactive and stay on top of mites. You won't kill them all once you have them, but you can minimize the problem.
