forcing extra amount but not on quotation

I took my Audi A4 to ensco engineering 27/03/2015 and we were and an amount of R4594, on Monday 30/03/2015 I took deposit R2000 and I was suppose to pay the remaining on 01/04/2015 when collecting but m now told I should pay R3047.62 and that was not on the initial quotation can you please please help as this is not fair as a customer