I think a simple solution would be is to have this so called friend talk to their support and have them physically close his account by their chat representative.
I did this because I told them I created another account by mistake and forgot the password for it so i created the one that I was talking to them with. They closed it and wasn't able to log into to it later when I did find the password while going thru some old documents on my desk.
It said a message something like "This account was inaccessible and is closed." So that confirms they did it and I continued using the new account which was using.
I think I did claim a 25 spin bonus on both of them. But never withdrawn from the old one.
So that might be the problem if they see the other one your friend had did a withdrawal of the bonus which was received.
You can try that if your friend can remember his password and get them to close it.
That might be your only other option.