Retriving my wifi account

Last year for the first time I got on line whilst on site, Southport I think it was. I couldn't purchase from the office and was advised to go on line to do it. Anyway I fumbled though and managed to secure £20 worth. Because I didn't go anywhere else where I could use the facility I still have about £18 left. I believe that it is accessible for twelve minths from the date of purchase? My query is "how do I access it"? I was given a number which I appear to have lost. Probably wrote it on a scrap piece of paper long discarded. Can anyone help?