Yes, you can easily do it. If it is possible to solve the problem without leaving the site, contact its support service. But if your complaint is ignored or rejected, then the issue goes to a more global level. Of course, you will not be able to contact the UK Gambling Commission, as it does not control the operation of such casinos. Instead, you can file a complaint with the organization that issued the licence or with one of the independent international bodies such as eCOGRA. You can be sure that your rights will be protected, and the disputable situation will be resolved as a result.
Also, to avoid possible unpleasant situations, try to choose reliable and reputable sites. They provide quality services and value every customer, so problems or reasons for complaints in such casinos are almost impossible. And these are the operators we recommend. We will never offer unverified or dishonest companies on this page.