MBD Debt Collectors harassment

MBD is collecting on behalf of Finchoice and they gave me a call with a double figure to what they suppose to collect from me. The person on the phone was rude and threatened me to accept the balance that is not correct. I asked them for a statement and they refusing but want me to accept a over charged balance. This is very bad because I can pay Finchoice what is exactly due to them without going through this harassment. Why do they have to make me pay double what I owe to make money and harass me over the phone.