but are you a UK citizen/resident? Were the passport you tried to submit a UK passport? if so, you might have broken their Terms and conditions. I've seen similar cases before that were posted here in the forum where the gambler is gambling in a country that is not restricted on the gambling site but the country where they are from is restricted.
I found this on the Terms and conditions
You are not allowed to register on the Website and use our services if you are a resident of Aruba, Australia, Belgium, Bonaire, Curacao, Cyprus, Denmark, Estonia, France, Germany, Hungary, Iran, Iraq, Italy, Netherlands, North Korea, Saba, Slovakia, Spain, St Maarten, Statia, Turkey, Ukraine, United Arab Emirates, U.S.A or the U.S.A dependencies, United Kingdom. We reserve the right to refuse customers from any other countries over and above the aforementioned jurisdictions at our own discretion.