Voucher still in date but the website says it has expired
I have a voucher code which was given to me at Thorpe Park with a valid date printed on it up to 31.12.2018. It is unused and I have only just sratched off the code number . When I put it into the website it's telling me that it is a time limited affer and it has expired.
I'm sure I am still in December 2018 so it should still work. Anyone give me any clues as to how to make it work?