Incorrect goods supp****

Hirsch's quoted and invoiced a Daikin FTXN35/RX35 airconditioning unit with installation but installed a RXN35KE unit instead which is an older unit to the one I was invoiced for. The unit now requires repairs and on enquiry with Daikin I find that the part on the older unit (the one that was installed) costs over R1,500 more than the unit that should have been installed. I have made numerous enquiries with Hirschs and esalated the matter and despite the sales consultant who sold me the unit acknowledging that the incorrect unit was installed senior management refuse to acknowledge any error on the part of Hirsch's.