Sport Nation Casino - Account closure and win confiscation without any proper justification

I deposited £500 with Sport Nation on 19/03/20 after receiving a bonus offer of 100% up to £500 (I can't remember if it was by text or email - I can't see the email in my Trash folder so may have been text). I had not used the Sport Nation site since I first created my account at the beginning of the year as they had not sent me any offers during that time, and since I had a recent large win at another casino I thought I would give them another go.

I used my £500 deposit on roulette over 2 numbers, and won £6300 - I withdrew the win straight away and forfeited the bonus.

The following day on 20/03/20 I received an email to say that my account had been closed, quoting site terms about "criminal or other suspicious activities" and "fraudulent, unlawful, dishonest or improper activity" without specifying what I had supposedly done wrong (see attachment "Sport Nation 20th Mar 2020 - account closure.jpg").

I replied to this straight away on 20/03/20 asking for clarification on if my win had been confiscated, and asking on what grounds my account had been closed, considering they were the ones sending me promo emails to entice me back. It took a week to get a reply, which stated that my email had been "escalated to a manager" and that someone would be in touch when it had been reviewed and investigated (see attachment "Sport Nation 20th March 2020 - reply.jpg").

On 23/03/20 I received £500 in my bank account, with no notification or other information, that was presumably a refund of my original cash deposit.

After waiting a further 10 days with no reply, I sent another email on 06/04/20 to ask for a reply, and received a reply the following day on 07/04/20 which just stated that my account had been closed as per the original email. No explanation or evidence of any investigation as I was promised, but confirming that my balance had been forfeited (see attachment "Sport Nation 6th April 2020.jpg").

I sent one final email on 08/04/20 expressing my frustration at having to chase for the promised reply and still not receiving any further explanation, and also pointing out that their actions didn't really follow the UK Gambling Commission guidelines for dealing with customer complaints, in an effort to push for answer, but received no further replies (see attachment "Sport Nation 8th April.jpg").

While I fully appreciate that accounts can be closed at the discretion of the operator, the circumstances around my account closure and the lack of information are not acceptable in my opinion. I would not have deposited at Sport Nation if they hadn't sent me a bonus offer - I'm pretty sure that this was the only time I have used their site since originally creating my account and claiming their welcome offer at the beginning of the year (I had issues getting the welcome bonus credited, which put me off using their site any more at the time as it took more than a week to get resolved if I remember correctly). To close my account without warning when I have legitimately won on a cash roulette spin without any proper explanation AND to claim my concerns would be investigated and then not to do so, and then refuse to reply any further shows poor customer service and does not comply with what I understood were a provider's obligations under UK Gambling Commission rules and regulations.