Child support is important in situations where parents share custody and in situations where one has limited visitation. While every situation is slightly different, child support is typically provided regardless of the amount of time the parents share with the child or children. Even if both parents share custody evenly, support can still be sought.
It is hard to deal with conflicts when a relationship is over. You may not want to see your ex-spouse, and it may be your priority to put any conflict to rest as quickly as you can. You just want to finalize the divorce, so you can move on with your life.
For a long time, your ex-spouse failed to pay any child support. Now that your child is older, the payments are finally being enforced. Your biggest issue with this is that your child has missed out on years of support from the other parent.