If you cant depend on Child Protective Services who can we go to?

My BF has 3 kids, who come to the house everyother weekend. Well the last past 4 weekends we had thm they would come with bruises in their inter thighs. This really pissed me off so i cant CPS thinking there would help alil or maybe even help to stop the abuse. Well we got them for 30 days for the summer. It is so happened the show up whn we have them so all the braising is gone. The caseworker talked to the mom and the mom convenced the caseworker we are just tryin to get out of child support. Which clearly is not the case. This girl is very conniving and a compulsive liar. Let me give you a far examples: The 8 yr old is on ADHD meds ok which she told me over the phone that hes on this meds so she can get an SSI check. (we have the for 3 weeks ann i have not popped one pill in his mouth and he's fine) example 2: I took xrated pics of me whn i first got with my BF and send them to his phone she got a hold of them printed them out and showed the whole town including her 8 yr old son. It was a secrect her told his dad. Wat kind of mother is that. Example 3: When my BF left her to be with me she packed her 8 yr old son clothes put thm in a bag and told him to get out and go be wit you dad at 10pm. He said she didnt let him back in the house til it was alrdy daylight (hes exact words) This is everything the 8 yr old boy tells us. The other 2 lil ones just sit there and say it happened at daycare. :( it breaks my heart to think the only i think we can count on to save these kids think it all about the money. We give this lady 306 every two weeks for these kids which is just 1/3 of my check. I dont need that money its for them its not like we're not paying it. But now the case worker is not answering our calls. Who can we go to now? Or can we request to chance caseworker? Plz help these kids go back home to this witch on the 14th. Please Help if you have an experance with CPS..