A ticket for the 20.12 will not be valid on 21.12. You could have refunded the ticket on the 19th, and bought a new one. Or just wait till you are in Switzerland. Normal Point-to-Point tickets are available at the same price at all times and therefore do not need to be bought in advance.
Refunding a ticket afterwards is not trivial, as you need to prove that you could not have used it. But you can always try. See here:
https://www.sbb.ch/en/help-and-contact/refunds-compensation/refunds-compensation/ticket-refunds.html
The railways do not provide wheelchairs.