No matter if there are alternative accounts or not, I don't like the approach this chat support is taking with the customer.
Players are paying their salary and still these "agents" reply in such a disrespectful manner, it's actually sad.

They could say something like: "We know you have multiple accounts, our system detected that because of shared IP/device or whatever. There is no arguing around it." or something like that. But repeating the same phrase like 5 times while giving no proof or anything is just garbage behavior.
Why do players always have to accept the OPINION of the casino I wonder. If they have proof they should show it. They player always gets the wrong end of the stick because they can't prove their innocence. The casino has all the cards in their hand and we are basically at their mercy.

I'm not saying the OP is right or the casino is right of course. I just don't like the unfair approach to cases like this. You have proof? Then show it. You can't show it? Well there is no proof then and the player deserves the money.