AFAIK that of 10€ means: no go, money gone. But there are NO direct trains L->C, its via Paris, change stations, then NoMAD-TER. OR maybe via direct TGV via/change Angers/Le Mans/Tours?

That of 20 you MAY have luck in exchange for other trip (but not money back) on a counter of SNCF-brush up your FRench.

It depends on where you booked your reservations. If you booked them via Interrail, it should have been possible via the Reservations Overview (if these reservations were refundable).