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.
It's being a resident of those restricted countries that is not allowed, as in accessing the sites while you're being in their soil, not for having those countries as your nationality. For example, a UK-born person are allowed to access the platform while he's taking vacation in Singapore [I... guess], or being an expatriat in Romania. So, unless OP left out some story here [like he actually accessed from UK, or something], that clause in their TnC is indeed not breached.