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.
Let me try to invite Razer here, he's usually very prompt.
Meanwhile, OP, does rollbit have a login sessions page where they provide the list of IP address that you use to access the platform? If they happen to have it [I think they do] and they happen to provide a list of the country of which those IPs are belong to and only if you're comfortable doing this, do you mind giving us a screenshot of this? With only the country being visible, and the rest of the IP address and details being censored. It'll help strengthen your case. And if they don't provide this kind of info, or if Razer feel the need to provide their own proof, do you give your consent to Razer to provide this list for us [with same sensitive data being blurred]?