Don't stand by their quotes...buyer beware!!

I wrote to Group 1 Renault, The Glen, on Thursday 13th April requesting prices on various filters for a Koleos. I received an e-mail requesting my VIN number which I sent through on Friday morning and the same afternoon I received an official quotation listing all the filters and their prices. I went through on Tuesday 18th April (2 working days later) to buy one of the filters. At the parts counter they used the quote I gave them to get the part number for the filter which was then brought through. I paid at the window and when I got back to my car looked at the invoice and found the cost of the filter had increased by just under 18%. I went back in but the parts desk had closed so I showed one of the Service Advisors the quote I had been sent plus the invoice. He said it was obviously an error, took photocopies of both, and said he would sort it out the next day. I heard nothing further the next day, not even a courtesy call to let me know it was, or was not, being resolved. Only after my following up with another email did I receive a reply that basically said ’‘the price on the invoice is correct and, if the price was discounted on the quote I should have informed them”. The quote, which he had used to obtain the part number, shows zero discount. I pointed this out in a reply email as well as the fact that both the quote and the invoice are pulled off the same database and the invoice cannot increase magically by 18%. To date I have received no further correspondence which, to be frank, is just telling me ”P*ss off… it is what it is. you pay what we tell you… not what was quoted”.