3% hydrogen peroxide isn't killing all of them either!
Have you tried anything other than peroxide?
My go-to is usually an essential oil, like neem, geranium, etc. Knocked a set of scale clean off, might work for these too.
Tho, Im looking at them, and they kinda look like some harmless bugs I have in my soil. I would check with an insect community for a more reliable id, because you may not need to worry about them