TC - I think you need to write a nasty letter to Easyjet HQ, addressed to the company secretary (look on Companies House website) with some words, in big bold capitals, like
"LETTER BEFORE ACTION - YOU MUST PAY MONEY WITHIN SEVEN CALENDAR DAYS OR ACTION MAY BE TAKEN THROUGH THE COURTS. YOU MAY HAVE TO PAY ADDITIONAL MONEY AS PART OF THE COURT PROCESS"
Not a nice thing to do... but usually quite effective
https://www.gov.uk/get-information-about-a-companyhttp://www.moneyclaim.gov.uk/web/mcol/welcomeOr, if you can't be bothered, have a chat with Bott & Co
https://www.bottonline.co.uk/