I signed up with Next Casino and received their Welcome Bonus. I completed the playthrough of the wagering requirements fully. A number of days after I tried to withdraw my winnings, the casino contacted me to say that I had breached one of their terms. I did not. This is the term in question -
10. Delaying any game round in any game, including free spins features and bonus features, to a later time when you have no more wagering requirement and/or performing new deposit(s) while having free spins features or bonus features still available in a game is prohibited. Players doing so agree to have their bonus and associated winnings declared void.
I have emailed Next Casino and asked them to explain exactly how and when I breached this condition but they have not replied. I am absolutely certain that I did not break this rule. I completed almost all of my wagering on one slot machine. I did not save up a bonus round to complete when the wagering requirement had been completed. I followed the rules properly and my winnings should not be withheld.