Train Fine Lost Ticket?

Hi All

Got my first letter for a train fine I got one Tuesday 11th of November. I paid for my ticket you get two a single and a return. I left my return at work and found it but have since then lost it because it has been so long. The stations are stevenage to Hertford north which is where is use to work. The distance is two stops takes 15 minutes. Stevenage is quite built up and normally has the barriers shut and always does in the morning . So I bought my ticket as you because the barriers are always closed and I would have to travel to work daily so of course I would buy one. The barriers where open and Hertford North on the way back so I didn't check my ticket after the train was delayed now they want me to pay an£120 fine for a £7.20 return ticket I paid but I'm 18 and don't have £120 I don't have money for a soliciter either what should i do plus I can't even travel to the location as it is off the main line