Western Dental Services review: fraudulent billing

Two of my children have been patients of WD for 4 mos. I have made payments on time each mo. for both thier braces, and received a letter from WD's collections dept. for one of the children. I continue to receive calls from a toll free #[protected]) that I cannot call back . So, I called their billing dept. [protected] to find out what happened with my pymt.: I was given the run around & had to answer fifty questions before I was told "We have a new billing system, you did incur a late fee; I'll go ahead and update the system". I need to know what happened to the cash pymt. that I made, and why a cash pymt. was posted on one of my child's account and not the other?