1win is having a good reputation here in the forum and also run a signature campaign here. $8000 is a lot of money. Have they returned your deposit of $5000 ? I know you cant access your account so if you can provide more details about your betting pattern on the site, it might help your case to gain some attention.
Re-uploading the screenshots for everyone to see. If you are really a long-time player, you have to prove that, like registration date, withdrawal, and deposit history; this is a violation of their terms. If they have solid proof, your chances are not good, and most of the time, they are right.