If it's been that long, then you can be fairly sure they have you marked as failing KYC. That would be why they won't talk to you anymore as well at a guess.
At any point in the conversations did you happen to say anything that could be construed as meaning you were unwilling or unable to supply whatever they had asked for? That could be one explanation for the closure, that is at least simple to address.
But them asking for selfies with all your docs makes me think they might suspect you are a gnome account for someone else. Or not the person shown on your docs. If you are betting their max limits, or maybe have changed your betting style in recent times, it can make them look for that issue.
As Semibluff said above, it also can be as simple as your photos not being accepted by the electronic ID verify software for tiny reasons, like a finger covering an edge.
Hopefully that helps give you some clues about what might be up. It will be easier to fix if you can work that out usually.
Your next step is to email
second_opinion@williamhill.co.uk and ask them to review what has been going on. Just tell them you don't understand what is going on and ask for help. As the best strategy to make sure you get a response. If they will not help you ask them how you can go about having IBAS review their decision. They should give you a code to use when submitting a dispute if needed at
https://www.ibas-uk.com/