WengenK The tickets I had purchased were from OUIGO, not from SNCF.
After OUIGO cancelled with little advance notice, we had to buy
tickets from SNCF and pay the walk-up price.
OUiGO is an SNCF brand, it is not a separate company. So in this case SNCF had to get you on another service, not you.
When a train gets cancelled, or a delay makes you miss a connection that these are your rights:
a) You can choose not to travel, in which case you get a refund. If the interruption happens on route you can decide to go back to where you started from free of charge, and claim a refund.
b) Or you continue your trip on another service in comparable circumstances. This may be even a service on another company if it is the only one available.
If the railway does not provide you with an alternative within 100 minutes you can make your own arrangements, and reclaim the costs, as long as the means used to get you to your destination are reasonable. So another train is perfectly fine. Chartering a private helicopter is not.
These regulations are set in law. Unfortunately the law does not require SNCF to inform you of these, and they do take advantage of that. Remember that SNCF considers passengers an unfortunately unavoidable nuisance. So you do have to stand on your rights at times. So in this case if indeed they did not rebook you what you should have done is request they pay you your new tickets back, not the original ones.
It is important to be aware that a cancellation of a train does not mean your ticket is cancelled. The railway cannot cancel your ticket at their own discretion. So the important thing is that you yourself do not get tricked in to cancelling.
The moment you cancel and accept a refund for the original tickert you lose your right to alternative routing. However from mine and other's experience if you show that you actually know what you are entitled to they will comply.