Billed more than Quotation

I booked a group B car for 3 days on their website and was quoted R538, Collected car on Thursday and on Sunday called OR Tambo branch to extend my booking to return car on Monday, to my shock I was told my total rental cost will be R1487. I send an email attaching email confirmation of my initial reservation confirming R538 and i also copied and pasted screen dumb of reservation on my profile on their website showing same amount got quoted. I have send numerous emails and made calls to their call centre with no joy as it seems nobody can help me with their mess. I received an invoice showing total cost as R1525 which includes also refuel servicing fee of R15.00, i filled up car at Engen garage at the airport what refuelling am i being charged? I did not quote myself and send myself an email confirmation of R538, why on earth am i being charged more than what i was quoted and how can they not sort this out. If i was quoted R1525 initially, there's no way i would have used Europcar i would have opted for another rental car company to get reasonable rates, i chose them based on the rates quoted. My first email to Europcar was on sunday today still not sorted out as yet