Keep a copy of the ticket, which is your contract. File a complaint with Small Claims in Manchester. You can do this online here...
https://www.moneyclaim.gov.uk/web/mcol/welcome
YOU WILL GET YOUR MONEY BACK and the cost of filing the court claim. The courts will enforce the contract written on the ticket. If the airline advised you this was the limit, bit must abide by this. You are a fool if you let this go.