Last term at uni it broke - there's a "lens error" or something. Took it into Jessops, and they said it'd cost about £120 [that I don't have] to fix...

Have come home and found the box, guarantee, etc but have no idea where the receipt might be... It was bought with vouchers.

What are the chances of them either believing me and replacing it, or being able to track down the purchase on the system and seeing it's still within guarantee?