First, child support is paid to the custodial parent to help raise the child. There doesn't have to be an accounting of what the mother is spending the money on. Unless the child is not being properly cared for.
If you feel that your child support is unfair, then go back to court and ask for a modification. If you can prove that the mother is spending money unwisely, prove it to the court.
If you aren't getting visitation, is there a court ordered visitation agreement? Then ask the court to enforce it.