I don’t think they can deny your withdrawal if you was playing with cash and not bonus funds.
You have be be very careful as it’s a common fraud that people will purposely self exclude themselves from said casinos and then go back on there gambling with maybe 1/2 details changed on the form.
If they win, they say nothing, if they lose they then email the casino requesting their deposits back and under UKGC protocol they have to do this.
I think they’ll withhold your winnings based on the fact you’re SE from their other site. Being that you have SE in the past, it’s important you check the terms and conditions before you start play, or to be double certain go to live support to see if you have SE in place on that site or connected sites.
Im sorry to say, but this could be an expensive lesson to check in future. The industry is absolutely rife with SE player fraud, as it’s on such a large scale, people who make genuine mistakes will be punished.
Rob