We can try to help you if you tell us more about what's going on. Why is it complicated?

Wagering requirements is 20x from 300balance, so 20x from 300 is 6000,so i win more than 20x,but when i withdraw,they say my balance must more than 15000 

U don't need to win u need to wager 20x ...that's a prob no1 there

second send exact screenshot of chat because 'must more than 15000' means nothng

third give a name of casino, 

and fourth , in every casino u need to deposit to make withdrawal, and u only can withdarwal % of

if that's Funclub casino (because they only gave 300 x 20 wager) u can only withdrawal 300 MAX after u deposit at least 20 or 50 i forgot... so do all this

According to what you're saying, I feel like you took some bonus and won while playing with the bonus. There are very often bonus terms applied to every bonus specifying the max. possible win, but since you didn't give us any info about the bonus, it's hard to say.

Definitely, we need more info to be able to help you.

At least in which casino did you play and which bonus you took.

I should say that casino is to take precautions