I have contacted the customer service since 08/10/2018 and 15/10/2018 because on Mafia I can't bet my Ms because you have to enter the bank details first and this operation is impossible to do, nothing opens. This problem persists, please do something. Thank you. Thank you.
The challenge is a daily ranking by game. The medals are used to rank you for the mega-challenge of the week (which therefore includes all the daily challenges).
The more medals you have, the higher your ranking.
As for customer service, you can contact them by going to''''''My account''' and then clicking on the submenu "Customer service" (last link).