The Child Maintenance Service is meant to make sure that parents who live apart from their children make regular payments to support them. But it stands accused of doing too little to enforce payments in some cases, leaving parents missing out on money they are legally entitled to. Meanwhile, parents who make payments say calculations done by the CMS can sometimes be wrong or unaffordable, and that mistakes can affect their mental health. Reporter Krupa Padhy meets parents on both sides to ask whether the system is failing both them and their children