So you are saying they mistakenly rain you around 3 btc and asking it back again? I think it is on you whether you want to give it back again or not. If you apply their terms, youbare suppose to say that they already lose it right? I know you can't withdraw it for sure as I know so instead of giving it back better if they lock on your account and both of you guys wont get nothing

Anyway I saw that they want to give you some bonus, do you even get it when you returning their money? If you get it then everything is already fix, nothing to be discussed again