Hi Sonavi,
To decide on what to compromise on (quality, dealine, cost) then you are going to need to know how the success of this project will be measured and the target values that equate to success. You say the "business wanted the system to be able to do the credit risk analysis of individual customers account" - why? What benefit is there to this? More customers? Lower risk loans?
Once you know which (or both or others) define the values that the business would agree means that the project can be defined as successful. For example 10% more customers, 20% reduction in loan defaulters, and so on. These are the project benefits and may have (should have!) already been defined.
Once you know the benefits, make an assessment of whether you can compromise quality and still get the benefits, or keep the dealines and still get the benefits or increase costs and still have a positive business case (over simplification: benefits minus costs).
Sometimes you can combine factors (lose a bit of quality and spend a bit more and take a bit more time) but sometimes you run up against constraints that mean you can't change these factors any further - e.g legal restrictions when calculating loans means that the quality cannot be cut back to a point where you can't demonstrate compliance with the law.
By the way, make sure that all who have the authority to directly or indirectly stop the project agree what the benefits are!
Hope that helps.
Guy