London Underground has nice clear policies around this, both about what you'll be charged

https://tfl.gov.uk/fares/how-to-pay-and-where-to-buy-tickets...

And about refunds (typically you'd get an automatic refund for a one-off event)

https://tfl.gov.uk/fares/refunds-and-replacements/touched-in...

I always have high levels of respect for companies with such clarity