they answered my mail.   

this is part of answer;

------------------In regards to the 10% weekly tennis cashback, "fortunately" you are not eligible for it. I mentioned fortunately because for you to be eligible for this promo you must have had losses on your tennis bets during the week, from Monday to Sunday, and that wasn´t the case. You won more than you lost. (You can check this info by accessing the "My bets" section and "My sports bets". --------------------------------------


Duelbits have this terms ;

How to take part:
1.Place one or more live or pre-match single bets on any tennis game no later than the 12th September.
2.We give you 10% cashback on your weekly net losses every Monday, up to $100
Make sure your email address is verified or your Steam account is on Level 10+ to receive your promotional reward.


But not clearly written in the terms and conditions... ( second term )

never mind..  good luck guys ..