Bajaj Finserv — wrong finance done by bajaj executive around three years ago

Address:

New Delhi, Delhi, 110062

I want to inform you that around 3 years ago i took a second hand phone from a shop which name is international value retail pvt. Ltd. So that time i don't had the that much of amount to buy that second hand phone. So i requested them for doing something so the manager of that shop and bajaj finserv executive done something (I don't know how they did). So i gave them 3 cheque and some docs in which signed by my younger brother and i told him " i am buying a second hand handset and he said ok. But instead of the old handest the bajaj executive and that manager financed a new samsung a-8 phone which was not in my knowledge and not also in my brother knowledge because we did not get any verification call for that mobile phone. So after doing that they said you need pay only 3 emi for this old handset which will goes from your account but now it's came to know they financed a new phone and bajaj asking for that emi the phone which we did not buy so i have so much tension what i have to do. How can i resolve the issue. Where should i make the complaint. Please help me.