First, check if you have enough funds in your account. You may be withdrawing more than what is available in your account. It is also possible that you still have an active bonus with unmet wagering requirements.
If the problem persists, get in touch with customer support. Click the “Help” tab and choose your preferred option to communicate. You can choose the Live Chat feature. It is the fastest but it is only available between 9:00 – 23:00 CET. Emails can be sent anytime but it will take longer to get a response.