If you want to submit a claim to SNCF for reimbursement, you need to fill in the required form [here] and return it by post to:
Service relations client SNCF 62973 ARRAS Cedex 9
Complaints concerning the conduct of an SNCF voyage are handled by SNCF’s Customer Relations Department (Service relations client SNCF).
To help process your application, be sure to include with your form all documents relating to your claim (original tickets, original invoice for any costs incurred ...). These must all be sent by post to the address above.