Payment of child support is not linked to ability to have visitation. If the court orders are in place and the best interest of the child is to permit said visitation, then the visitation shall continue. If the noncustodial parent is changing days and conducting himself in a manner that is detrimentally affecting the child, then you may have a basis for a modification of the visitation. Failure to pay ordered support is punishable by contempt. If you live in the Los Angeles area and the court's order was entered in Los Angeles, you can present the order to the DIstrict Attorney's office, Child Support Division for enforcement and they will help you take steps to collect without cost.
Yes. If you do not cooperate in the visitation and sharing of custody per the court Order you are in contempt. Presumably it is in the child's best interest to visit with his or her father regardless of how much money he sends you.
Dad, of course, is in contempt every month he does not pay support, but it is up to you to sue him for the money. He is building up a big debt to you with interest. Hopefully he fins work soon and starts to catch up on his payments.