Multi account is truly forbidden in almost all of the casino but in any case that their claims is wrong and you didn't have any alt account on their site then the best solution is to talk their support and ask politely with your current issues.
But if you truly do it on purpose then you should not react about that since that will mostly happen when a casino/casino sportsbook do when they found that theirs a illegal activity happening in their site.
If OP didn't actually do it then it's possible that this was their scheme but a lot of this happened before and it just proves that they really commit to make another account that's why they got banned or their account was closed. If talking to support politely will help to solve the problem then he shouldn't be here now complaining/reporting the scam accusation on the said casino site.
what a paradox
The bookmaker writes to me that he is 100% sure that I have another account. and as proof, he says - you have vpn!
you understand that this cannot be 100% proof !!
it sounds like cheating!
I write in response that I am ready for any checks! I don't have any other accounts!
Why does everyone write only bad things here?
Return my money!
You should read before you write something.
This is their reply
"We have 100% evidence that this user has multiple accounts.
He created an account before, deposit and withdraw without any problems. We gave this user a bonus.
After he meet the roll over requirements, 2 other users in a few days asks also for the bonuses.
When we were checking these accounts, it turns out that this is the same user.
We have 100% proof based on IP address, and this users also uses VPN to hide his real location which is also not allowed(which he admitted by himself already)
I can not provide usernames here in the topic, but we have all the evidence and their accounts remain closed and the funds will be held by Adkinsbet.
This is also the wrong thread."
They did not write their 100% proof was based on the VPN. They write that you were also using VPN. Probably you did not use the VPN the whole time, and then they saw your real IP address.
The professional gambling cheaters group are looking for new ways how to steal money from a site, but it seems Adkinsbet is catching them every time!
That should be a good lesson for those guys, but some people will never learn it.
You manipulated the location with your VPN from another country, to hide Russia.
They have the right to close your account.
What people forget here is that it seems the case that you are using like 4/5 accounts trying to get the bonus and then withdraw the funds. And after it, repeat the procedure.
Do you really think you could get away with that?