An account closure is always possible in the section "Responsible Gaming" -> My Settings.
You can exclude your account permanently or for a certain period. You can choose between twenty-four (24) hours, seven (7) days, thirty (30) days, six (6) weeks or six (6) months.
If you want to self-exclude permanently, please go to the section "Quasargaming Services & Limits" on the same page.
Please be aware that this is a serious action which is not easily undone.