First, raise the issue with the operator through its own complaints procedure — most operators publish a dedicated mailbox and a timeframe for first response. Keep the ticket number, the dates and screenshots of the conversation; they are what the escalation body will ask for later.
If the operator's answer is final and you still disagree, the UK route is Alternative Dispute Resolution: an independent body approved by the Gambling Commission reviews the file and issues a decision binding on the operator. ADR is free to the player; the operator pays the case fee.
We can rewrite an article if the facts turn out to be wrong, and we can flag a pattern of complaints to our readership — but we cannot move money, release a bonus or reopen an account. Those tickets belong with the operator and, if needed, with the ADR body.
IBAS (ibas-uk.com) and ProMediate (promediate.co.uk) are the two ADR bodies most often used by UK-licensed operators. The operator's own terms and conditions name the ADR body that will hear your case; use the one named there.
The operator must reply to a complaint within eight weeks under its UK licence. If no final response arrives in that window, you can escalate to ADR immediately. ADR itself aims to issue a decision within 90 days of accepting the case.
Hold on to everything: the deposit history that preceded the dispute, the ticket IDs the operator issued, every chat transcript and every email in both directions. An ADR body can only rule on what it sees, and operators sometimes close support tickets without saving the earlier messages. If a transcript starts to disappear, take a screenshot before the window refreshes.
A final note on expectations. ADR decisions are binding on the operator but not on the player: if the ruling goes against you, you can still take the matter to court. That is a bigger step and worth taking only when a lot of money is at stake; most ordinary disputes are resolved at the ADR stage and resolved reasonably quickly.