Small black worms on my cactus

[Spookids]

I recently got myself two small indoor cacti and have run into problems already with one. I do not know the type of either, but suspect the affected one to be a hedgehog cactus. Yesterday (when in old pot) I found a little black worm in the soil. I rushed to clean, insecticide (kinda, the only thing I have currently is rose clear) and repot into a new pot. Today while cleaning the dirt off my cactus I spotted another, but smaller. I removed it but am very worried and sad, I don't want my cacti to die. I am new to having cacti and am your classic broke college student who can't afford expensive systemic pesticides. Any help is hugely appreciated ☺

[purpleinopp]

If some critter is living in the soil, changing the soil would get rid of it.