Can an online bookmaker void an already paid winning bet?

Yesterday evening I decided to bet in-play on tennis. I made different bets, won a few and got them paid as normal. However when I checked my account today I noticed that my balance was significantly less than what I had yesterday. I checked my bet history and my biggest winning bet which was paid yesterday is now void and the money was taken back from my account. When I click on the bet, I can see the following message:

"Reason for voiding: An obvious mistake - the bet has been placed after the outcome was known"

Isn't that just stealing? Can I do anything to get my money back?