Help: betting company wants to take back my wins

(England) im using an online betting app for a year now or two placing small bets on parlays from time to time. Last week i played a card game and managed to cash out huge amount- i still have pending money on my account when they suspended it. Now they emailed me saying there was a malfunction in the game and i need to return the money or else they will get it back from my bank account.

I just find it unfair whenever you win they do stuff like this. Im just an ordinary person who just got lucky. Can they take it back from my bank account? Should i get a solicitor at this time?

So for context: I played live blackjack behind bet. I placed my bets on all hands and just go with the flow whether the main player will hit or stay.

Update: i already got intouch with a solicitor coz they keep on emailing me everyday to return my winnings asap.