Horrible service from Chery.

This is for the horrible service I received at Chery Shelly Beach(KZN). I went to this dealership as I was interested in a Chery Tiggo 7, the lady at the finance Dept named Sindy assisted me with a quote of R4800 installment after paying a deposit of R140 000 of which I was happy with, I submitted all the necessary documents that were requested and I paid the deposit, I was then informed that the car will be ready on Friday the 18th of Nov for collection as they didn't have the color I wanted.

My Joy of buying a new car turned sour when Sindy told me on collection day that she calculated wrong, the installment was not R4800 but over R5000 and the car's selling price was now inflated by R50 000, I didn't have a choice but to agree as I had sold my previous car to pay the deposit that we had agreed on, how is it that she realised on collection day that she calculated wrong whereas I've been communicating with them for close to two weeks? or is this the strategy Chery uses to trap consumers into signing deals they are not happy with. I'm really not happy with how this enfolded coz should I have known sooner about the "correct" installment I wouldn't have bought the car.