Before I mistakenly gave your casino a shot, I was using Gamdom, and they support multiple accounts & are one of the biggest casinos in the space.
Before creating an account in any casino, it is most important to read the T&C of that casino properly. But you missed everything here. T&C may be different from one casino to another, it is not good to ignore T&C while creating account on assumption which may lead to problems at one time. You're in that problem now and the casinos will take advantage because they have you to catch, and that's what they're doing.