Poor service of repair

to apply new grit coating onto areas that are damaged and to supply 2 coats of Harveycote black paint well after 6 working days spread over two weeks due to rain. they informed me that the job was done I inspected the roof and on each roof damage did not have the grit when the manager came to check I was told he had put 4 coats of paint on I refused to pay as it was not as stated in the written quote now I'm about to be sued !!!!! The manager became very aggressive trying to forceme to pay the rest of the quote....