Returning of a pass

Hello, we bought an Interrail ticket plus for our son Joris in July. He was supposed to use it for a language study trip to England. Unfortunately, the interrail accounts on all possible trains were already fully booked, which is why he could not travel by train. We would therefore like to have the ticket refunded. As a precaution, we bought the plus version, but when you log on to their site and try to return the ticket, it always says: You currently have no orders eligible for a refund. How can we return the pass and get the money refunded? Pass number: G7T1JX Sincerely Marcus Bürger