Cat just gave birth...but she is not feeding her three kittens...wtf.what should i do?

we found her under the bed with three kittens.we got them together and she picked them up to move them she wouldn't feed so we bought kitten formula we attempted to feed them but the mom Deedee was all over them and stared to meeeeow a lot.we put her in the bathroom with her kids but she was trying to break the door down ad we let her out whats going on how do i do this i want the kittens to live...and i work at petco.so i can get any matrial.