You should ask for a rakeback since you lost that much... There needs to be one.
They're pretty legit in my eyes, used a deposit code and won 800 euro, withdrawed and it worked but thats nothing in comparison what you played with.
I once lost 20k on a roulette site, asked for a rakeback and got 5k back so...

Try it atleast
....and maybe stop depositing on that site and try to enjoy gamble again, don't gamble with the imagination of getting your lost money back, have fun gambling that should be the main reason you do it.