Child protective services is a joke

BG
I called them to report that my niece and nephew were being abused and they won't do an investigation because I don't have specific dates! 
Over Christmas break my niece and nephew (they both told me separately from each other and did not have time to talk to each other between when they told me) told me that their parents "hit, punch, strangle, and verbally abuse them. They tell my niece and nephew that they hate them and wish they were never born. I have see. Both parents he verbally abusive and it has always made me so angry. When the kids told me they also physically anise them I decided it was time to call cps. Their mom is in rehab right now for alcohol abuse, but has still been verbally abusice and their dad has them full time. Their dad drives drunk with the every night and their mom got a duo last year but has been driving drunk with them in the car (without a license) up until she went to rehab. 
Anyway..... I called cps and they said they would get back with me. After a week I got a call saying that since they didn't have specific dates they would not be doing an investigation (my niece and nephew at 9 and 11.... They don't know the date half the time and when they told me what was going on they acted like it was normal) I am so sick about this! Do any of you have suggestions?