Ok, so the train company has taken the piss on everyone relying on the cap or buying Travelcards from Epsom.
I usually relied on the off-peak cap on my Railcard-discounted Oyster card to cap on zone 1-9 for Epsom in the past, although I haven’t been there recently.
And now suddenly they have removed the validity of zone 1-9 Travelcard there and can now penalty fare anyone who use his usual ticket to commute to, or through, Epsom, without making any public announcement that the station is rezoned.