quotation change

I got a quotation for paving to the value of R8300.00 written by hurbert on the back of his card, which i accepted,after the job was done and i went to pay ,the price rose to R9724.00 why the extra R1400.00. I have phoned them ,sent messages ,spoke to him on the phone and even sat waiting at his office,even spoke to him at a dealer in town where i met him . promises were made to come and explain the diffirence but up to now nothing happened (it is now three months after the job was done and the conversstion with him!