Hacked contact list by loan app

Hi , I have experience some fraudulent like I have taken loan some minimal amount from zype application. last three months I have paid emi correctly. but this month my emi got delayed by 7 days. They are very dangerous they called my family and others people's. but one thing I'm not understanding that I am not giving any reference number to them from the time of applying loan application but I'm not understanding how they take the numbers? any how they hacked my contact list?? can anyone please tell me , how is it possible??