Free Traffic Legal Advice

Hi, my son received a parking fine around February saying he was parked in Southampton illegally from  Company called Civil Enforcement who after goggling looked like a scam company , the thing is that my Son was in South America at the time of the offence and his van was parked up at his house in Bournemouth, we are now getting letters from dcbl with Final Reminder letters , i tried calling to explain but they just said they would continue to persue and would not listen , just think its crazy but unsure what to do next?